Detect <link rel='manifest'> and notify embedder.

Source/core/core.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',
             'animation/TimedItem.idl',
             'animation/Timeline.idl',
             'animation/Timing.idl',
@@ skipping 2433 matching lines @@
             'html/HTMLViewSourceDocument.h',
             'html/HTMLWBRElement.cpp',
             'html/HTMLWBRElement.h',
             'html/ImageData.cpp',
             'html/ImageData.h',
             'html/ImageDocument.cpp',
             'html/ImageDocument.h',
             'html/LabelableElement.cpp',
             'html/LabelsNodeList.cpp',
             'html/LabelsNodeList.h',
+            'html/LinkManifest.cpp',
+            'html/LinkManifest.h',
             'html/LinkRelAttribute.cpp',
             'html/LinkRelAttribute.h',
             'html/LinkResource.cpp',
             'html/LinkResource.h',
             'html/MediaController.cpp',
             'html/MediaController.h',
             'html/MediaDocument.cpp',
             'html/MediaDocument.h',
             'html/MediaError.h',
             'html/MediaFragmentURIParser.cpp',
@@ skipping 915 matching lines @@
             'html/track/vtt/VTTScannerTest.cpp',
             'loader/MixedContentCheckerTest.cpp',
             'rendering/RenderOverflowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }