Limit drawing operations to the width/height of the IOSurface. b=570347 r=josh

gfx/src/thebes/utils/nsCoreAnimationSupport.mm

@@ -690,6 +690,13 @@ nsresult nsCARenderer::DrawSurfaceToCGContext(CGContextRef aContext,
     return NS_ERROR_FAILURE;
   }
 
+  // We get rendering glitches if we use a width/height that falls
+  // outside of the IOSurface.
+  if (aWidth > ioWidth - aX) 
+    aWidth = ioWidth - aX;
+  if (aHeight > ioHeight - aY) 
+    aHeight = ioHeight - aY;
+
   CGImageRef cgImage = ::CGImageCreate(ioWidth, ioHeight, 8, 32, bytesPerRow,
               aColorSpace, kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host,
               dataProvider, NULL, true, kCGRenderingIntentDefault);
@@ -706,10 +713,8 @@ nsresult nsCARenderer::DrawSurfaceToCGContext(CGContextRef aContext,
     return NS_ERROR_FAILURE;
   }
 
-  ::CGContextTranslateCTM(aContext, 0.0f, float(aHeight));
   ::CGContextScaleCTM(aContext, 1.0f, -1.0f);
-  ::CGContextTranslateCTM(aContext, aX, -aY);
-  CGContextDrawImage(aContext, CGRectMake(0, 0, aWidth, aHeight), subImage);
+  ::CGContextDrawImage(aContext, CGRectMake(aX, -aY-aHeight, aWidth, aHeight), subImage);
 
   ::CGImageRelease(subImage);
   ::CGImageRelease(cgImage);