Move WebGraphicsContext3D related tests from web/tests/ to platform/graphics/gpu/

Source/platform/blink_platform.gypi

Index: Source/platform/blink_platform.gypi
diff --git a/Source/platform/blink_platform.gypi b/Source/platform/blink_platform.gypi
index 5874fe93fbfdfaf945fdeb2b0cb12172ba1b2b9b..29f1155bf1ffe25951ae1a02deff90ad26e966fa 100644
--- a/Source/platform/blink_platform.gypi
+++ b/Source/platform/blink_platform.gypi
@@ -913,10 +913,14 @@
     # NOTE: these are legacy unit tests, do not add more!
     'platform_web_unittest_files': [
       'animation/TimingFunctionTest.cpp',
+      'graphics/Canvas2DLayerBridgeTest.cpp',
+      'graphics/Canvas2DLayerManagerTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
+      'graphics/gpu/DrawingBufferTest.cpp',
       'graphics/test/MockImageDecoder.h',
+      'graphics/test/MockWebGraphicsContext3D.h',
     ],
   },
 }