MediaStream API: Implement Navigator.getMediaDevices

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 252 matching lines @@
       'exported/WebData.cpp',
       'exported/WebDeviceMotionData.cpp',
       'exported/WebDeviceOrientationData.cpp',
       'exported/WebFileSystemCallbacks.cpp',
       'exported/WebFilterKeyframe.cpp',
       'exported/WebFloatQuad.cpp',
       'exported/WebHTTPBody.cpp',
       'exported/WebHTTPLoadInfo.cpp',
       'exported/WebImageSkia.cpp',
       'exported/WebMediaConstraints.cpp',
+      'exported/WebMediaDeviceInfo.cpp',
       'exported/WebMediaStream.cpp',
       'exported/WebMediaStreamSource.cpp',
       'exported/WebMediaStreamTrack.cpp',
       'exported/WebMediaStreamTrackSourcesRequest.cpp',
       'exported/WebPrerender.cpp',
       'exported/WebPrerenderingSupport.cpp',
       'exported/WebRTCConfiguration.cpp',
       'exported/WebRTCICECandidate.cpp',
       'exported/WebRTCSessionDescription.cpp',
       'exported/WebRTCSessionDescriptionRequest.cpp',
@@ skipping 616 matching lines @@
       'animation/TimingFunctionTestHelper.cpp',
       'animation/TimingFunctionTestHelper.h',
       'animation/TimingFunctionTestHelperTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/test/MockImageDecoder.h',
     ],
   },
 }