compositor-worker: plumb element id and mutable properties

third_party/WebKit/Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
       'ColorChooserPopupUIController.cpp',
       'ColorChooserPopupUIController.h',
@@ skipping 242 matching lines @@
       'LinkHighlightImplTest.cpp',
       'PageOverlayTest.cpp',
       'WebDragDataTest.cpp',
       'WebEmbeddedWorkerImplTest.cpp',
       'WebNodeTest.cpp',
       'WebElementTest.cpp',
       # FIXME: Move the tests from web/tests/ to appropriate places.
       # crbug.com/353585
       'tests/ActivityLoggerTest.cpp',
       'tests/ChromeClientImplTest.cpp',
+      'tests/CompositorWorkerTest.cpp',
       'tests/DocumentLoaderTest.cpp',
       'tests/DocumentLoadingRenderingTest.cpp',
       'tests/FakeWebPlugin.cpp',
       'tests/FakeWebPlugin.h',
       'tests/FrameLoaderClientImplTest.cpp',
       'tests/FrameTestHelpers.cpp',
       'tests/FrameTestHelpers.h',
       'tests/FrameThrottlingTest.cpp',
       'tests/ImeOnFocusTest.cpp',
       'tests/KeyboardTest.cpp',
@@ skipping 48 matching lines @@
         {
           'web_unittest_files': [
             # Mac uses ScrollAnimatorMac instead of ScrollAnimator.
             'tests/ScrollAnimatorTest.cpp',
           ],
         }
       ],
     ],
   },
 }