Bug 1059450 - Fix shape dimension in BackButton (r=mcomella)

mobile/android/base/toolbar/BackButton.java

@@ -49,10 +49,10 @@ public class BackButton extends ShapedButton {
         super.onSizeChanged(width, height, oldWidth, oldHeight);
 
         mPath.reset();
-        mPath.addCircle(width/2, height/2, width/2 - mBorderWidth, Path.Direction.CW);
+        mPath.addCircle(width/2, height/2, width/2, Path.Direction.CW);
 
         mBorderPath.reset();
-        mBorderPath.addCircle(width/2, height/2, (width/2) - mBorderWidth, Path.Direction.CW);
+        mBorderPath.addCircle(width/2, height/2, (width/2) - (mBorderWidth/2), Path.Direction.CW);
     }
 
     @Override