Fix edge case bugs of canvas arc.

Source/core/platform/graphics/Path.cpp

 /*
  * Copyright (C) 2003, 2006 Apple Computer, Inc.  All rights reserved.
  *                     2006 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 258 matching lines @@
 void Path::addArcTo(const FloatPoint& p1, const FloatPoint& p2, float radius)
 {
     m_path.arcTo(p1, p2, WebCoreFloatToSkScalar(radius));
 }
 
 void Path::closeSubpath()
 {
     m_path.close();
 }
 
-void Path::addArc(const FloatPoint& p, float r, float sa, float ea, bool anticlockwise)
+void Path::addArc(const FloatPoint& p, float radius, float startAngle, float endAngle, bool anticlockwise)
 {
     SkScalar cx = WebCoreFloatToSkScalar(p.x());
     SkScalar cy = WebCoreFloatToSkScalar(p.y());
-    SkScalar radius = WebCoreFloatToSkScalar(r);
+    SkScalar radiusScalar = WebCoreFloatToSkScalar(radius);
     SkScalar s360 = SkIntToScalar(360);
 
     SkRect oval;
-    oval.set(cx - radius, cy - radius, cx + radius, cy + radius);
+    oval.set(cx - radiusScalar, cy - radiusScalar, cx + radiusScalar, cy + radiusScalar);
 
-    float sweep = ea - sa;
-    SkScalar startDegrees = WebCoreFloatToSkScalar(sa * 180 / piFloat);
+    float sweep = endAngle - startAngle;
+    SkScalar startDegrees = WebCoreFloatToSkScalar(startAngle * 180 / piFloat);
     SkScalar sweepDegrees = WebCoreFloatToSkScalar(sweep * 180 / piFloat);
     // Check for a circle.
     if (sweepDegrees >= s360 || sweepDegrees <= -s360) {
         // Move to the start position (0 sweep means we add a single point).
         m_path.arcTo(oval, startDegrees, 0, false);
         // Draw the circle.
         m_path.addOval(oval, anticlockwise ?
             SkPath::kCCW_Direction : SkPath::kCW_Direction);
         // Force a moveTo the end position.
         m_path.arcTo(oval, startDegrees + sweepDegrees, 0, true);
@@ skipping 113 matching lines @@
 {
     m_path.offset(WebCoreFloatToSkScalar(size.width()), WebCoreFloatToSkScalar(size.height()));
 }
 
 bool Path::unionPath(const Path& other)
 {
     return Op(m_path, other.m_path, kUnion_PathOp, &m_path);
 }
 
 }