<rdar://problem/8272978>
https://bugs.webkit.org/show_bug.cgi?id=43665

Reviewed by Anders Carlsson.

- Adds support for delete key going back (mac only for now)
- Adds support for command-left/command right going back/forward
- Flesh out scrolling due to arrow keys on the mac to match old webkit.
- Made performDefaultBehaviorForKeyEvent platform specific and added
  a boolean return value which will be used later to inform the UI process
  about what events have been processed.

* Shared/CoreIPCSupport/WebPageProxyMessageKinds.h:
(WebPageProxyMessage::):
* UIProcess/API/mac/WKView.mm:
(-[WKView _wantsKeyDownForEvent:]):
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::didReceiveSyncMessage):
* WebProcess/WebPage/WebBackForwardListProxy.cpp:
(WebKit::WebBackForwardListProxy::backItem):
(WebKit::WebBackForwardListProxy::forwardItem):
* WebProcess/WebPage/WebPage.cpp:
(WebKit::WebPage::keyEvent):
* WebProcess/WebPage/WebPage.h:
* WebProcess/WebPage/mac/WebPageMac.mm:
(WebKit::scroll):
(WebKit::WebPage::performDefaultBehaviorForKeyEvent):
* WebProcess/WebPage/qt/WebPageQt.cpp:
(WebKit::scroll):
(WebKit::WebPage::performDefaultBehaviorForKeyEvent):
* WebProcess/WebPage/win/WebPageWin.cpp:
(WebKit::scroll):
(WebKit::WebPage::performDefaultBehaviorForKeyEvent):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@64918 268f45cc-cd09-0410-ab3c-d52691b4dbfc