Implement basic parts of hit regions on canvas2d.

Source/platform/graphics/Path.h

Index: Source/platform/graphics/Path.h
diff --git a/Source/platform/graphics/Path.h b/Source/platform/graphics/Path.h
index 431f03d206cb85bf96fcece92237ce572b5482d4..7d360c7a1270263f04d4bc8716294a9b3df9f209 100644
--- a/Source/platform/graphics/Path.h
+++ b/Source/platform/graphics/Path.h
@@ -143,6 +143,8 @@ public:
     void addPathForRoundedRect(const FloatRect&, const FloatSize& topLeftRadius, const FloatSize& topRightRadius, const FloatSize& bottomLeftRadius, const FloatSize& bottomRightRadius);
     void addBeziersForRoundedRect(const FloatRect&, const FloatSize& topLeftRadius, const FloatSize& topRightRadius, const FloatSize& bottomLeftRadius, const FloatSize& bottomRightRadius);
 
+    bool subtractPath(const Path&);
+
     // Updates the path to the union (inclusive-or) of itself with the given argument.
     bool unionPath(const Path& other);