Remove CSS clients of ImageResource

sky/engine/core/core.gni

Index: sky/engine/core/core.gni
diff --git a/sky/engine/core/core.gni b/sky/engine/core/core.gni
index fc8649e404c759b9ba4219a31b9f66a5d50d34e5..4847195755fd22bf068a59e68ad773d02079fe09 100644
--- a/sky/engine/core/core.gni
+++ b/sky/engine/core/core.gni
@@ -65,8 +65,6 @@ sky_core_files = [
   "animation/animatable/AnimatableDouble.h",
   "animation/animatable/AnimatableFilterOperations.cpp",
   "animation/animatable/AnimatableFilterOperations.h",
-  "animation/animatable/AnimatableImage.cpp",
-  "animation/animatable/AnimatableImage.h",
   "animation/animatable/AnimatableLength.cpp",
   "animation/animatable/AnimatableLength.h",
   "animation/animatable/AnimatableLengthBox.cpp",
@@ -121,8 +119,6 @@ sky_core_files = [
   "css/CSSCalculationValue.h",
   "css/CSSComputedStyleDeclaration.cpp",
   "css/CSSComputedStyleDeclaration.h",
-  "css/CSSCrossfadeValue.cpp",
-  "css/CSSCrossfadeValue.h",
   "css/CSSCustomFontData.h",
   "css/CSSFilterValue.cpp",
   "css/CSSFilterValue.h",
@@ -146,10 +142,6 @@ sky_core_files = [
   "css/CSSHelper.h",
   "css/CSSImageGeneratorValue.cpp",
   "css/CSSImageGeneratorValue.h",
-  "css/CSSImageSetValue.cpp",
-  "css/CSSImageSetValue.h",
-  "css/CSSImageValue.cpp",
-  "css/CSSImageValue.h",
   "css/CSSInheritedValue.cpp",
   "css/CSSInheritedValue.h",
   "css/CSSInitialValue.cpp",
@@ -950,10 +942,6 @@ sky_core_files = [
   "rendering/style/StyleBoxData.cpp",
   "rendering/style/StyleBoxData.h",
   "rendering/style/StyleDifference.h",
-  "rendering/style/StyleFetchedImage.cpp",
-  "rendering/style/StyleFetchedImage.h",
-  "rendering/style/StyleFetchedImageSet.cpp",
-  "rendering/style/StyleFetchedImageSet.h",
   "rendering/style/StyleFilterData.cpp",
   "rendering/style/StyleFilterData.h",
   "rendering/style/StyleFlexibleBoxData.cpp",