Implement contextmenu attribute with basic support of <menu>

Source/core/core.gypi

 {
     'includes': [
       'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationPlayer.idl',
@@ skipping 88 matching lines @@
             'events/FocusEvent.idl',
             'events/HashChangeEvent.idl',
             'events/KeyboardEvent.idl',
             'events/MessageEvent.idl',
             'events/MouseEvent.idl',
             'events/MutationEvent.idl',
             'events/OverflowEvent.idl',
             'events/PageTransitionEvent.idl',
             'events/PopStateEvent.idl',
             'events/ProgressEvent.idl',
+            'events/RelatedEvent.idl',
             'events/ResourceProgressEvent.idl',
             'events/SecurityPolicyViolationEvent.idl',
             'events/TextEvent.idl',
             'events/TouchEvent.idl',
             'events/TransitionEvent.idl',
             'events/UIEvent.idl',
             'events/WebKitAnimationEvent.idl',
             'events/WheelEvent.idl',
             'fileapi/Blob.idl',
             'fileapi/File.idl',
@@ skipping 49 matching lines @@
             'html/HTMLInputElement.idl',
             'html/HTMLKeygenElement.idl',
             'html/HTMLLIElement.idl',
             'html/HTMLLabelElement.idl',
             'html/HTMLLegendElement.idl',
             'html/HTMLLinkElement.idl',
             'html/HTMLMapElement.idl',
             'html/HTMLMarqueeElement.idl',
             'html/HTMLMediaElement.idl',
             'html/HTMLMenuElement.idl',
+            'html/HTMLMenuitemElement.idl',
             'html/HTMLMetaElement.idl',
             'html/HTMLMeterElement.idl',
             'html/HTMLModElement.idl',
             'html/HTMLOListElement.idl',
             'html/HTMLObjectElement.idl',
             'html/HTMLOptGroupElement.idl',
             'html/HTMLOptionElement.idl',
             'html/HTMLOptionsCollection.idl',
             'html/HTMLOutputElement.idl',
             'html/HTMLParagraphElement.idl',
@@ skipping 305 matching lines @@
             'events/FocusEvent.idl',
             'events/HashChangeEvent.idl',
             'events/KeyboardEvent.idl',
             'events/MessageEvent.idl',
             'events/MouseEvent.idl',
             'events/MutationEvent.idl',
             'events/OverflowEvent.idl',
             'events/PageTransitionEvent.idl',
             'events/PopStateEvent.idl',
             'events/ProgressEvent.idl',
+            'events/RelatedEvent.idl',
             'events/ResourceProgressEvent.idl',
             'events/SecurityPolicyViolationEvent.idl',
             'events/TextEvent.idl',
             'events/TouchEvent.idl',
             'events/TransitionEvent.idl',
             'events/UIEvent.idl',
             'events/WebKitAnimationEvent.idl',
             'events/WheelEvent.idl',
             'html/MediaKeyEvent.idl',
             'html/canvas/WebGLContextEvent.idl',
@@ skipping 1731 matching lines @@
             'events/NodeEventContext.cpp',
             'events/NodeEventContext.h',
             'events/OverflowEvent.cpp',
             'events/OverflowEvent.h',
             'events/PageTransitionEvent.cpp',
             'events/PageTransitionEvent.h',
             'events/PopStateEvent.cpp',
             'events/PopStateEvent.h',
             'events/ProgressEvent.cpp',
             'events/ProgressEvent.h',
+            'events/RelatedEvent.cpp',
+            'events/RelatedEvent.h',
             'events/ResourceProgressEvent.cpp',
             'events/ResourceProgressEvent.h',
             'events/ScopedEventQueue.cpp',
             'events/ScopedEventQueue.h',
             'events/SecurityPolicyViolationEvent.h',
             'events/TextEvent.cpp',
             'events/TextEvent.h',
             'events/ThreadLocalEventNames.h',
             'events/TouchEvent.cpp',
             'events/TouchEvent.h',
             'events/TouchEventContext.cpp',
             'events/TouchEventContext.h',
             'events/TransitionEvent.cpp',
             'events/TransitionEvent.h',
             'events/TreeScopeEventContext.cpp',
             'events/TreeScopeEventContext.h',
             'events/UIEvent.cpp',
             'events/UIEventWithKeyState.cpp',
             'events/WebKitAnimationEvent.cpp',
             'events/WebKitAnimationEvent.h',
             'events/WheelEvent.cpp',
             'events/WheelEvent.h',
             'events/WindowEventContext.cpp',
             'events/WindowEventContext.h',
         ],
         'webcore_html_files': [
             'html/ClassList.cpp',
             'html/ClassList.h',
+            'html/CustomContextMenuProvider.cpp',
+            'html/CustomContextMenuProvider.h',
             'html/DOMFormData.cpp',
             'html/DOMFormData.h',
             'html/DocumentNameCollection.cpp',
             'html/DocumentNameCollection.h',
             'html/FormAssociatedElement.cpp',
             'html/FormDataList.cpp',
             'html/FormDataList.h',
             'html/HTMLAllCollection.cpp',
             'html/HTMLAllCollection.h',
             'html/HTMLAnchorElement.cpp',
@@ skipping 74 matching lines @@
             'html/HTMLLinkElement.h',
             'html/HTMLMapElement.cpp',
             'html/HTMLMapElement.h',
             'html/HTMLMarqueeElement.cpp',
             'html/HTMLMarqueeElement.h',
             'html/HTMLMediaElement.cpp',
             'html/HTMLMediaSource.cpp',
             'html/HTMLMediaSource.h',
             'html/HTMLMenuElement.cpp',
             'html/HTMLMenuElement.h',
+            'html/HTMLMenuitemElement.cpp',
+            'html/HTMLMenuitemElement.h',
             'html/HTMLMetaElement.h',
             'html/HTMLMeterElement.cpp',
             'html/HTMLMeterElement.h',
             'html/HTMLModElement.cpp',
             'html/HTMLModElement.h',
             'html/HTMLNameCollection.cpp',
             'html/HTMLNameCollection.h',
             'html/HTMLNoEmbedElement.cpp',
             'html/HTMLNoEmbedElement.h',
             'html/HTMLNoScriptElement.cpp',
@@ skipping 1018 matching lines @@
             'loader/MixedContentCheckerTest.cpp',
             'page/NetworkStateNotifierTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }