[chromium] Add empty WebCompositorFrame/WebCompositorFrameAck https://bugs.webkit.org/show_bug.cgi?id=98841 Reviewed by James Robinson. These were used in the WebKit API but never defined. * chromium/public/WebCompositorFrame.h: Added. (WebKit): * chromium/public/WebCompositorFrameAck.h: Added. (WebKit): git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@130945 268f45cc-cd09-0410-ab3c-d52691b4dbfc