Web Animations: Remove confusing interpolation subdirectory.

Source/core/core.gypi

 {
     'includes': [
       'core_generated.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',
@@ skipping 662 matching lines @@
             'animation/css/CSSAnimationData.cpp',
             'animation/css/CSSAnimationData.h',
             'animation/css/CSSAnimations.cpp',
             'animation/css/CSSAnimations.h',
             'animation/css/CSSPropertyEquality.cpp',
             'animation/css/CSSPropertyEquality.h',
             'animation/css/CSSTimingData.cpp',
             'animation/css/CSSTimingData.h',
             'animation/css/CSSTransitionData.cpp',
             'animation/css/CSSTransitionData.h',
-            'animation/interpolation/DefaultStyleInterpolation.h',
-            'animation/interpolation/DeferredLegacyStyleInterpolation.h',
-            'animation/interpolation/DeferredLegacyStyleInterpolation.cpp',
-            'animation/interpolation/Interpolation.cpp',
-            'animation/interpolation/Interpolation.h',
-            'animation/interpolation/LegacyStyleInterpolation.h',
-            'animation/interpolation/LengthStyleInterpolation.cpp',
-            'animation/interpolation/LengthStyleInterpolation.h',
-            'animation/interpolation/StyleInterpolation.h',
+            'animation/DefaultStyleInterpolation.h',
+            'animation/DeferredLegacyStyleInterpolation.h',
+            'animation/DeferredLegacyStyleInterpolation.cpp',
+            'animation/Interpolation.cpp',
+            'animation/Interpolation.h',
+            'animation/LegacyStyleInterpolation.h',
+            'animation/LengthStyleInterpolation.cpp',
+            'animation/LengthStyleInterpolation.h',
+            'animation/StyleInterpolation.h',
             'clipboard/DataObject.cpp',
             'clipboard/DataObject.h',
             'clipboard/DataObjectItem.cpp',
             'clipboard/DataObjectItem.h',
             'clipboard/DataTransfer.cpp',
             'clipboard/DataTransfer.h',
             'clipboard/DataTransferItem.cpp',
             'clipboard/DataTransferItem.h',
             'clipboard/DataTransferItemList.cpp',
             'clipboard/DataTransferItemList.h',
@@ skipping 2657 matching lines @@
             'animation/AnimationTranslationUtilTest.cpp',
             'animation/CompositorAnimationsTest.cpp',
             'animation/CompositorAnimationsTestHelper.h',
             'animation/CompositorAnimationsTimingFunctionReverserTest.cpp',
             'animation/EffectInputTest.cpp',
             'animation/InterpolableValueTest.cpp',
             'animation/InterpolationEffectTest.cpp',
             'animation/KeyframeEffectModelTest.cpp',
             'animation/TimingCalculationsTest.cpp',
             'animation/TimingInputTest.cpp',
-            'animation/interpolation/DeferredLegacyStyleInterpolationTest.cpp',
-            'animation/interpolation/LengthStyleInterpolationTest.cpp',
+            'animation/DeferredLegacyStyleInterpolationTest.cpp',
+            'animation/LengthStyleInterpolationTest.cpp',
             'css/AffectedByFocusTest.cpp',
             'css/CSSCalculationValueTest.cpp',
             'css/CSSFontFaceTest.cpp',
             'css/CSSParserValuesTest.cpp',
             'css/CSSSelectorTest.cpp',
             'css/CSSTestHelper.cpp',
             'css/CSSTestHelper.h',
             'css/CSSValueTestHelper.h',
             'css/DragUpdateTest.cpp',
             'css/MediaValuesTest.cpp',
@@ skipping 40 matching lines @@
             'rendering/RenderOverflowTest.cpp',
             'rendering/RenderTableCellTest.cpp',
             'rendering/RenderTableRowTest.cpp',
             'rendering/shapes/BoxShapeTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }