Reviewed by David Hyatt.

        Enhance the hit testing to take a rectangle instead of a point
        https://bugs.webkit.org/show_bug.cgi?id=40197

        The primary goal of this change is to provide mechanisms for more precise tap
        actions by the users on mobile devices.

        Patch extends the hit testing system to work considering a rectangular area
        as input instead of a point, when applicable. For that, the HitTestResult class
        was modified to take a padding (IntSize). The padding specifies a fuzzy range for
        accepting input events in pixels coordinates for both vertical and horizontal
        orientations. In other words, it tells how much to expand the search rect
        around a supposed touch point.

        If it non-positive, hit testing will behavior as the current point based hit testing,
        and methods are no-op'ed to not regress this common behavior performance-wise.
        When positive IntSize is provided, the hit test result will keep record of all
        nodes that intersect the built up test area. The logic will continue searching when it
        finds a candidate until the rectangle is fully enclosed by the boundaries of a candidate.
        The result will be a list of nodes in the z-order they are hit-tested.
        Caller will decide how to process them.

        In order to expose the functionality, the patch:

        - Adds a nodesFromRect method to the Document class, exposing the funcionality
        to the DOM. Method returns a NodeList with all nodes that intersect the given
        hit-tested area.
        - Extends hitTestResultAtPoint method of the EventHandler with an extra 'padding'
        parameter, defaulting to IntSize(0, 0). The rect-based hit test is performed when a
        positive padding is passed in.

        Test: fast/dom/nodesFromRect-basic.html

        * WebCore.base.exp:
        * dom/Document.cpp:
        (WebCore::Document::nodesFromRect): This method exposes the rect based funcionality to
        the DOM. It works similarly to elementFromPoint, however receiving a rectangular area
        as input instead of a point, and returning a z-index ordered list of nodes (not elements)
        whose area intersect the hit test rect.
        * dom/Document.h: Ditto.
        * dom/Document.idl: Ditto.
        * page/EventHandler.cpp:
        (WebCore::EventHandler::hitTestResultAtPoint): The funcionality is also exposed through this
        method. Patch adds a additional IntSize parameter to work as the padding area, building up
        the hit test rect.
        * page/EventHandler.h: Ditto.
        * rendering/HitTestResult.cpp:
        (WebCore::HitTestResult::HitTestResult): Rect based hit test constructor. Receives a
        padding IntSize as parameter. It can be (0,0).
        (WebCore::HitTestResult::operator=): Modified to assign the m_rectBasedTestResult as well.
        (WebCore::HitTestResult::append): Merge to HitTestResult objects in a way that the
        list node's of both objects get amended.
        (WebCore::HitTestResult::addNodeToRectBasedTestResult): Adds a given Node to the list of
        hit nodes.
        * rendering/HitTestResult.h:
        (WebCore::HitTestResult::padding): Returns the padding as an IntSize.
        (WebCore::HitTestResult::isRectBasedTest): Returns if the HitTestResult is rect based or not.
        (WebCore::HitTestResult::.rectBasedTestResult): Returns the list nodes hit.
        (WebCore::HitTestResult::rectFromPoint): Returns the hit test rect given the hit test point
        and padding.
        * rendering/RenderLayer.cpp:
        (WebCore::RenderLayer::hitTestLayer):
        (WebCore::RenderLayer::hitTestList):
        (WebCore::RenderLayer::hitTestChildLayerColumns):
        * rendering/EllipsisBox.cpp:
        (WebCore::EllipsisBox::nodeAtPoint): Method is modified to support rect based hit test extension.
        Now it not just checks if the boundary of the node being hit-tested contains a hit test point, but
        instead it checks if the boundary of the node intersects a hit test rect. It is implemented so
        that the common case (point based hit test) works as previously.
        * rendering/InlineFlowBox.cpp:
        (WebCore::InlineFlowBox::nodeAtPoint): Ditto.
        * rendering/InlineTextBox.cpp:
        (WebCore::InlineTextBox::nodeAtPoint): Ditto.
        * rendering/RenderBlock.cpp:
        (WebCore::RenderBlock::nodeAtPoint): Ditto.
        (WebCore::RenderBlock::hitTestColumns): Ditto.
        * rendering/RenderBox.cpp:
        (WebCore::RenderBox::nodeAtPoint): Ditto.
        * rendering/RenderImage.cpp:
        (WebCore::RenderImage::nodeAtPoint): Ditto.
        * rendering/RenderLineBoxList.cpp:
        (WebCore::RenderLineBoxList::hitTest):
        * rendering/RenderSVGRoot.cpp:
        (WebCore::RenderSVGRoot::nodeAtPoint): Ditto.
        * rendering/RenderTable.cpp:
        (WebCore::RenderTable::nodeAtPoint): Ditto.
        * rendering/RenderTableSection.cpp:
        (WebCore::RenderTableSection::nodeAtPoint): Ditto.
        * rendering/RenderWidget.cpp:
        (WebCore::RenderWidget::nodeAtPoint): Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@64272 268f45cc-cd09-0410-ab3c-d52691b4dbfc