Fix use-of-uninitialized-value in TransformationMatrix::blend()

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 898 matching lines @@
       'graphics/filters/ImageFilterBuilderTest.cpp',
       'graphics/gpu/DrawingBufferTest.cpp',
       'graphics/test/MockDiscardablePixelRef.h',
       'image-decoders/ImageDecoderTest.cpp',
       'mac/ScrollElasticityControllerTest.mm',
       'network/HTTPParsersTest.cpp',
       'testing/ArenaTestHelpers.h',
       'testing/TreeTestHelpers.cpp',
       'testing/TreeTestHelpers.h',
       'transforms/TransformOperationsTest.cpp',
+      'transforms/TransformationMatrixTest.cpp',
       'text/BidiResolverTest.cpp',
       'text/DateTimeFormatTest.cpp',
       'text/SegmentedStringTest.cpp',
       'text/UnicodeUtilitiesTest.cpp',
       'weborigin/DatabaseIdentifierTest.cpp',
       'weborigin/KURLTest.cpp',
       'weborigin/OriginAccessEntryTest.cpp',
       'weborigin/SecurityOriginTest.cpp',
       'weborigin/SecurityPolicyTest.cpp',
     ],
     # NOTE: these are legacy unit tests, do not add more!
     'platform_web_unittest_files': [
       'graphics/BitmapImageTest.cpp',
       'graphics/Canvas2DLayerBridgeTest.cpp',
       'graphics/Canvas2DLayerManagerTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/GraphicsLayerTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }