Add path option(path2d) for hit regions on canvas2d.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 933275c0f1bb0eb8ece6ccc861e0124b756fc810..c42d58574469c8e8921db970bc9babba6f76aa00 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -2373,16 +2373,24 @@ void CanvasRenderingContext2D::addHitRegion(const Dictionary& options, Exception
         return;
     }
 
+    RefPtr<Path2D> path2d;
+    options.getWithUndefinedOrNullCheck("path", path2d);
+
+    Path specifiedPath;
+    if (path2d)
+        specifiedPath = path2d->path();
+    else
+        specifiedPath = m_path;
+

[c.shu, 2014/07/01 02:03:28]

The above can be simplified as
Path specifiedPath = path2d ? path2d->path() : m_path;

[zino, 2014/07/01 05:37:28]

Done.

     FloatRect clipBounds;
     GraphicsContext* context = drawingContext();
 
-    if (m_path.isEmpty() || !context || !state().m_invertibleCTM
+    if (specifiedPath.isEmpty() || !context || !state().m_invertibleCTM
         || !context->getTransformedClipBounds(&clipBounds)) {
         exceptionState.throwDOMException(NotSupportedError, "The specified path has no pixels.");

[Rik, 2014/06/30 16:42:00]

I know this isn't part of this CL but we really shouldn't throw here.

[zino, 2014/07/01 05:37:28]

I'm not sure but,
According to the spec, if the specified path has no pixels,
throw a NotSupportedError exception and abort these steps.

         return;
     }
 
-    Path specifiedPath = m_path;
     specifiedPath.transform(state().m_transform);
 
     if (context->isClipMode()) {