Fix CopyFromBackingStore giving back empty SkBitmaps on mac.

content/browser/renderer_host/compositing_iosurface_mac.mm

Index: content/browser/renderer_host/compositing_iosurface_mac.mm
diff --git a/content/browser/renderer_host/compositing_iosurface_mac.mm b/content/browser/renderer_host/compositing_iosurface_mac.mm
index 84441ef2ca1f7dd9d7e5c9e13721a98a3e195053..890fd8356711683a73944c2e0a8b7bfbd5c5bd09 100644
--- a/content/browser/renderer_host/compositing_iosurface_mac.mm
+++ b/content/browser/renderer_host/compositing_iosurface_mac.mm
@@ -865,11 +865,14 @@ void CompositingIOSurfaceMac::FinishCopy() {
   }
   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0); CHECK_GL_ERROR();
 
+  // Ref so they don't get deleted in CleanupResourcesForCopy.
   base::Callback<void(bool, const SkBitmap&)> callback = copy_context_.callback;
+  SkBitmap out_buf = copy_context_.out_buf;
+
   CleanupResourcesForCopy();
   CGLSetCurrentContext(0);
 
-  callback.Run(buf != NULL, copy_context_.out_buf);
+  callback.Run(buf != NULL, out_buf);
 }
 
 void CompositingIOSurfaceMac::CleanupResourcesForCopy() {