Adjust the CoreGraphics context for offscreen layers.

skia/ext/skia_utils_mac.mm

Index: skia/ext/skia_utils_mac.mm
===================================================================
--- skia/ext/skia_utils_mac.mm	(revision 115549)
+++ skia/ext/skia_utils_mac.mm	(working copy)
@@ -307,13 +307,13 @@
 void SkiaBitLocker::releaseIfNeeded() {
   if (!cgContext_)
     return;
-  canvas_->getDevice()->accessBitmap(true).unlockPixels();
+  canvas_->getTopDevice()->accessBitmap(true).unlockPixels();
   CGContextRelease(cgContext_);
   cgContext_ = 0;
 }
 
 CGContextRef SkiaBitLocker::cgContext() {
-  SkDevice* device = canvas_->getDevice();
+  SkDevice* device = canvas_->getTopDevice();
   DCHECK(device);
   if (!device)
     return 0;
@@ -334,8 +334,10 @@
   // Apply clip in device coordinates.
   CGMutablePathRef clipPath = CGPathCreateMutable();
   SkRegion::Iterator iter(canvas_->getTotalClip());
+  const SkIPoint& pt = device->getOrigin();
   for (; !iter.done(); iter.next()) {
-    const SkIRect& skRect = iter.rect();
+    SkIRect skRect = iter.rect();
+    skRect.offset(-pt);
     CGRect cgRect = SkIRectToCGRect(skRect);
     CGPathAddRect(clipPath, 0, cgRect);
   }
@@ -344,7 +346,8 @@
   CGPathRelease(clipPath);
 
   // Apply content matrix.
-  const SkMatrix& skMatrix = canvas_->getTotalMatrix();
+  SkMatrix skMatrix = canvas_->getTotalMatrix();
+  skMatrix.postTranslate(-SkIntToScalar(pt.fX), -SkIntToScalar(pt.fY));
   CGAffineTransform affine = SkMatrixToCGAffineTransform(skMatrix);
   CGContextConcatCTM(cgContext_, affine);