add optional origin parameter to accessTopLayerPixels

BUG=skia:
R=bsalomon@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/244763004

git-svn-id: http://skia.googlecode.com/svn/trunk@14290 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index c57ae9a..e8da129 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1106,8 +1106,12 @@
     return dev ? dev->peekPixels(info, rowBytes) : NULL;
 }
 
-void* SkCanvas::accessTopLayerPixels(SkImageInfo* info, size_t* rowBytes) {
-    return this->onAccessTopLayerPixels(info, rowBytes);
+void* SkCanvas::accessTopLayerPixels(SkImageInfo* info, size_t* rowBytes, SkIPoint* origin) {
+    void* pixels = this->onAccessTopLayerPixels(info, rowBytes);
+    if (pixels && origin) {
+        *origin = this->getTopDevice(false)->getOrigin();
+    }
+    return pixels;
 }
 
 void* SkCanvas::onAccessTopLayerPixels(SkImageInfo* info, size_t* rowBytes) {