IDL: Put generated union type containers in separate files

Source/core/html/canvas/CanvasRenderingContext2D.h

Index: Source/core/html/canvas/CanvasRenderingContext2D.h
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.h b/Source/core/html/canvas/CanvasRenderingContext2D.h
index 2d67e2cfc98bf10116296de37f00dcc63cc0bdff..2be287a96aa177fb906685e9fcca7e5f94518450 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.h
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.h
@@ -27,7 +27,7 @@
 #define CanvasRenderingContext2D_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
-#include "bindings/core/v8/UnionTypesCore.h"
+#include "bindings/core/v8/StringOrCanvasGradientOrCanvasPattern.h"
 #include "core/css/CSSFontSelectorClient.h"
 #include "core/html/canvas/Canvas2DContextAttributes.h"
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
@@ -62,6 +62,7 @@ class ExceptionState;
 class FloatRect;
 class HTMLCanvasElement;
 class HTMLImageElement;
+class HTMLImageElementOrHTMLVideoElementOrHTMLCanvasElementOrImageBitmap;
 class HTMLVideoElement;
 class ImageData;
 class TextMetrics;