Fix edge case bugs of canvas arc.

Source/core/html/canvas/CanvasPathMethods.h

 /*
  * Copyright (C) 2006, 2007, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2012, 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 29 matching lines @@
 class CanvasPathMethods {
 public:
     virtual ~CanvasPathMethods() { }
 
     void closePath();
     void moveTo(float x, float y);
     void lineTo(float x, float y);
     void quadraticCurveTo(float cpx, float cpy, float x, float y);
     void bezierCurveTo(float cp1x, float cp1y, float cp2x, float cp2y, float x, float y);
     void arcTo(float x0, float y0, float x1, float y1, float radius, ExceptionCode&);
-    void arc(float x, float y, float r, float sa, float ea, bool anticlockwise, ExceptionCode&);
+    void arc(float x, float y, float radius, float startAngle, float endAngle, bool anticlockwise, ExceptionCode&);
     void rect(float x, float y, float width, float height);
 
     virtual bool isTransformInvertible() const { return true; }
 
 protected:
     CanvasPathMethods() { }
     Path m_path;
 };
 }
 
 #endif