Allow the creation of a skia::PlatformCanvas from a CGContextRef.

skia/ext/platform_canvas.cc

Index: skia/ext/platform_canvas.cc
diff --git a/skia/ext/platform_canvas.cc b/skia/ext/platform_canvas.cc
index 44b0d161e380ae4d0625c6ede684a01e3be3ab8f..b3577e56cb8e76d38810e5e8aacb9711dae0cc1b 100644
--- a/skia/ext/platform_canvas.cc
+++ b/skia/ext/platform_canvas.cc
@@ -32,4 +32,13 @@ size_t PlatformCanvas::StrideForWidth(unsigned width) {
   return 4 * width;
 }
 
+bool PlatformCanvas::initializeWithDevice(SkDevice* device) {
+  if (!device)
+    return false;
+
+  setDevice(device);
+  device->unref();  // Was created with refcount 1, and setDevice also refs.
+  return true;
+}
+
 }  // namespace skia