https://bugs.webkit.org/show_bug.cgi?id=127015

Reviewed by Benjamin Poulain.

This is the first step towards adding support for selections in
non editable content on iOS for WK2.
In particular, this patch adds the basic plumbing to decide which
gesture recognizers are enabled and adds empty stubs for the gestures
that we'll need to support.
There are two separate assistants for selections, one to be used
in editable text (UIWKTextInteractionAssistant) and one for non editable
text (UIWKSelectionAssistant) and they are mutually exclusive.
UIWKSelectionAssistant is created at the time the view is created, 
and swapped with UIWKTextInteraction assistant
only when an editable element is focused and the keyboard appears on screen.

gestureRecognizerShouldBegin is the delegate call used to decide which gestures
should begin based on the position the gesture occurred at.
We want to avoid as much as possible synchronous calls to the WebProcess to
retrieve information about the content and in order to do so, we take advantage
of the order in which the gesture recognizers will trigger, based on the delay
configured at initialization.
The first gesture to trigger is highlightLongPress, followed by longpress in the
active assistant and longpress in the WKInteractionView.
There are two different scenarios for highlighlongpress based on which assistant is
currently active.

UIWKSelectionAssistant is active:
    We send a request to the WebProcess to get information on the position
    and we return YES, allowing the gesture to start.
    We delegate to the WebProcess the proper handling of highlight based on the element.
    When longPress gesture fires for the assistant, we assume we have received the reply to our
    previous request, if not we fetch the information synchronously.
    We are then able to make an informed decision about whether
    or not to start the gesture. If the reply is NO, the third and last long press
    gesture can be evaluated to decide whether to show the action sheet or simply generate
    a click event.

UIWKTextInteractionAssistant is active:
    In this case we must have information about the position immediately and we issue
    a synchronous request to the WebProcess.
    If we are not interacting with the same node, we return NO.
    Then the longpress gesture fires for the assistant which performs the same check.
    If the node is the same, the loupe gesture will start, otherwise the last longpress
    gesture will be evaluated to decide about showing the action sheet or generating a
    click event.

* Scripts/webkit2/messages.py:
* Shared/InteractionInformationAtPosition.cpp: Added.
(WebKit::InteractionInformationAtPosition::encode):
(WebKit::InteractionInformationAtPosition::decode):
* Shared/InteractionInformationAtPosition.h: Added.
(WebKit::InteractionInformationAtPosition::InteractionInformationAtPosition):
* UIProcess/API/ios/PageClientImplIOS.h:
* UIProcess/API/ios/PageClientImplIOS.mm:
(WebKit::PageClientImpl::positionInformationDidChange):
* UIProcess/API/ios/WKContentView.mm:
(-[WKContentView _positionInformationDidChange:]):
* UIProcess/API/ios/WKContentViewInternal.h:
* UIProcess/API/ios/WKInteractionView.h:
* UIProcess/API/ios/WKInteractionView.mm:
(-[WKInteractionView initWithFrame:]):
(-[WKInteractionView dealloc]):
(-[WKInteractionView gestureRecognizer:canPreventGestureRecognizer:]):
(-[WKInteractionView gestureRecognizer:canBePreventedByGestureRecognizer:]):
(isSamePair):
(-[WKInteractionView gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:]):
(-[WKInteractionView _showImageSheet]):
(-[WKInteractionView _showLinkSheet]):
(-[WKInteractionView _actionForLongPress]):
(-[WKInteractionView ensurePositionInformationIsUpToDate:]):
(-[WKInteractionView gestureRecognizerShouldBegin:]):
(-[WKInteractionView hasSelectablePositionAtPoint:]):
(-[WKInteractionView pointIsInAssistedNode:]):
(-[WKInteractionView _longPressRecognized:]):
(-[WKInteractionView _doubleTapRecognized:]):
(-[WKInteractionView _twoFingerDoubleTapRecognized:]):
(-[WKInteractionView _twoFingerPanRecognized:]):
(-[WKInteractionView useSelectionAssistantWithMode:]):
(-[WKInteractionView _positionInformationDidChange:]):
(-[WKInteractionView interactionAssistant]):
(-[WKInteractionView _startAssistingKeyboard]):
(-[WKInteractionView _stopAssistingKeyboard]):
* UIProcess/PageClient.h:
* UIProcess/WebPageProxy.h:
* UIProcess/WebPageProxy.messages.in:
* UIProcess/ios/WebPageProxyIOS.mm:
(WebKit::WebPageProxy::didReceivePositionInformation):
(WebKit::WebPageProxy::getPositionInformation):
(WebKit::WebPageProxy::requestPositionInformation):
* WebKit2.xcodeproj/project.pbxproj:
* WebProcess/WebPage/WebPage.h:
* WebProcess/WebPage/WebPage.messages.in:
* WebProcess/WebPage/ios/WebPageIOS.mm:
(WebKit::WebPage::selectWithGesture):
(WebKit::WebPage::getPositionInformation):
(WebKit::WebPage::requestPositionInformation):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162103 268f45cc-cd09-0410-ab3c-d52691b4dbfc