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

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 2355 matching lines @@
 {
     HitRegionOptions passOptions;
 
     options.getWithUndefinedOrNullCheck("id", passOptions.id);
     options.getWithUndefinedOrNullCheck("control", passOptions.control);
     if (passOptions.id.isEmpty() && !passOptions.control) {
         exceptionState.throwDOMException(NotSupportedError, "Both id and control are null.");
         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()) {
         // FIXME: The hit regions should take clipping region into account.
         // However, we have no way to get the region from canvas state stack by now.
         // See http://crbug.com/387057
         exceptionState.throwDOMException(NotSupportedError, "The specified path has no pixels.");
         return;
     }
 
@@ skipping 45 matching lines @@
 
 unsigned CanvasRenderingContext2D::hitRegionsCount() const
 {
     if (m_hitRegionManager)
         return m_hitRegionManager->getHitRegionsCount();
 
     return 0;
 }
 
 } // namespace WebCore