Reviewed by Maciej.

        Fix for <rdar://problem/5472062> -webkit-user-select: none makes selection difficult
        and for <rdar://problem/5472056> REGRESSION: Cannot type into edit fields on a form (sccsheriff.org)

        Tests:

        This fix has a few steps:
        1) Removes the ignore value for the -webkit-user-select property.  We now decide when to prevent selection from starting by calling canStartSelection on the node.
        2) Implements canStartSelection which returns false for all elements that used to have -webkit-user-select:ignore set, true for content editable nodes, 
           and walks up the tree to ask the parent before allowing selection to be started on any other nodes.
        3) We used to disallow selection from starting within -webkit-user-select:none blocks, but now we only use canStartSelection for that.  This will allow easy selections
           in cases like iChat where there's a mix of selectable and non-selectable content.
        4) Makes -webkit-user-select inherited.  After removing the "ignore" value, -webkit-user-select would behave like it was inherited anyways since we already allowed the text value to override the none value.


        * css/html4.css: Removed all usage of -webkit-user-select: ignore.  This is now handled internally with canStartSelection().
          Now -webkit-user-select won't be unintentionally overridden by nodes that don't want to allow selection to be started, but do want to honor the -webkit-user-select to
          determine whether or not selection is allowed at all.

        * editing/SelectionController.cpp: (WebCore::SelectionController::selectAll):
          Don't try to determine whether selection is allowed inside the root node here.  VisiblePosition and Selection creation will keep Selection endpoints out of -webkit-user-select:none regions.
        
        * dom/Node.h:
        * dom/Node.cpp: (WebCore::Node::canStartSelection): Added. Always allows selection to be started in a content editable node.  If there's a parent, ask the parent if starting a selection is allowed.
          If there's no parent, default to allowing selection.
        * html/HTMLAnchorElement.h:
        * html/HTMLAnchorElement.cpp: (WebCore::HTMLAnchorElement::canStartSelection): Added. If its not a link, then calls the base class. Disallows selection for non-editable links.
          Allows selection for editable links.
          This logic used to be done in CSSStyleSelector by changing the user-select property.
        * html/HTMLButtonElement.h: (WebCore::HTMLButtonElement::canStartSelection): Added. Disallows selection from starting in buttons.
        * html/HTMLImageElement.h: (WebCore::HTMLImageElement::canStartSelection): Added. Disallows selection from starting in images.
        * html/HTMLInputElement.h:
        * html/HTMLInputElement.cpp: (WebCore::HTMLInputElement::canStartSelection): Added. Disallows selection from anything that's not a text field.  Text fields call up to the base class.
          When they're editable, text controls will always be selectable because of the case for content editable content. Otherwise, they'll respect their parent element's decision about starting a selection. 
        * html/HTMLSelectElement.h: (WebCore::HTMLSelectElement::canStartSelection): Added. Disallows selection from starting in popup buttons.

        * page/EventHandler.cpp:
        (WebCore::EventHandler::selectClosestWordFromMouseEvent): Use canMouseDownStartSelect instead of the ambiguously named shouldSelect().
        (WebCore::EventHandler::handleMousePressEventTripleClick): ditto.
        (WebCore::EventHandler::handleMousePressEventSingleClick): ditto.
        (WebCore::EventHandler::updateSelectionForMouseDrag): Use canMouseDragExtendSelect.
        (WebCore::EventHandler::selectCursor): Paint an ibeam in any region that allows you to click to create a selection.
        (WebCore::EventHandler::canMouseDownStartSelect): Now fires the selectStart event, and calls canStartSelection instead of checking the user-select property.
        (WebCore::EventHandler::canMouseDragExtendSelect): This is identical to canMouseDownStartSelect because of 12823, even though it seems strange that we would fire the selectStart event here.
        * page/EventHandler.h:
        * page/FocusController.cpp: (WebCore::clearSelectionIfNeeded): Calls canStartSelection instead of checking the user-select property to decide when to prevent selection creation. 
        * rendering/RenderObject.cpp: (WebCore::RenderObject::draggableNode): ditto.
        * rendering/RenderObject.h: Removed helper methods that are no longer needed.

        * rendering/RenderStyle.h: Made userSelect inherited.  After removing the "ignore" value, -webkit-user-select would behave like it was inherited 
          anyways since we already allowed the text value to override the none value.
          Removed the SELECT_AUTO and SELECT_IGNORE values since they're no longer used.
        (WebCore::):
        (WebCore::RenderStyle::userSelect):
        (WebCore::RenderStyle::setUserSelect):
        (WebCore::RenderStyle::initialUserSelect):
        * rendering/RenderStyle.cpp:
        (WebCore::StyleRareNonInheritedData::StyleRareNonInheritedData):
        (WebCore::StyleRareNonInheritedData::operator==):
        (WebCore::StyleRareInheritedData::StyleRareInheritedData):
        (WebCore::StyleRareInheritedData::operator==):
        (WebCore::RenderStyle::diff):

        * css/CSSComputedStyleDeclaration.cpp: (WebCore::CSSComputedStyleDeclaration::getPropertyCSSValue): Remove case for SELECT_AUTO and SELECT_IGNORE
        * css/CSSStyleSelector.cpp:
        (WebCore::CSSStyleSelector::adjustRenderStyle):  Remove adjustment for links.  This is now handled in HTMLAnchorElement::canStartSelection.
        (WebCore::CSSStyleSelector::applyProperty): Map CSS_VAL_AUTO to SELECT_TEXT.  Remove CSS_VAL_IGNORE.

LayoutTests:

        Reviewed by Maciej.

        Tests for <rdar://problem/5472062> -webkit-user-select: none makes selection difficult
        and for <rdar://problem/5472056> REGRESSION: Cannot type into edit fields on a form (sccsheriff.org)

        * fast/css/computed-style-expected.txt: Updated for default -webkit-user-select value.
        * fast/css/computed-style-without-renderer-expected.txt: ditto.

        * editing/selection/5333725.html: Re-enabled.
        * editing/selection/5333725.html-disabled: Removed.

        * editing/selection/user-select-text-inside-user-select-ignore.html-disabled: Removed. Adjusted this test to be more specific and renamed it to textfield-inside-anchor. 
        * editing/selection/user-select-text-inside-user-select-ignore-expected.txt: Removed. 
        * fast/forms/textfield-inside-anchor-expected.txt: Added.
        * fast/forms/textfield-inside-anchor.html: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@25641 268f45cc-cd09-0410-ab3c-d52691b4dbfc