Make reftests work for sky.

sky/viewer/viewer.cc

Index: sky/viewer/viewer.cc
diff --git a/sky/viewer/viewer.cc b/sky/viewer/viewer.cc
index eb5b6d0fba31b3bb14f243cf89fbfd4146359401..4c5dd74eb292dcbce3c546cbebbf0f1e8432948f 100644
--- a/sky/viewer/viewer.cc
+++ b/sky/viewer/viewer.cc
@@ -13,6 +13,8 @@
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/public/cpp/application/interface_factory_impl.h"
 #include "mojo/services/content_handler/public/interfaces/content_handler.mojom.h"
+#include "sky/compositor/display_delegate_bitmap.h"
+#include "sky/compositor/display_delegate_ganesh.h"
 #include "sky/engine/public/web/Sky.h"
 #include "sky/viewer/content_handler_impl.h"
 #include "sky/viewer/document_view.h"
@@ -24,6 +26,9 @@
 
 namespace sky {
 
+// Load the viewer in testing mode so we can dump pixels.
+const char kTesting[] = "--testing";
+
 class Viewer : public mojo::ApplicationDelegate,
                public mojo::InterfaceFactory<mojo::ContentHandler> {
  public:
@@ -34,6 +39,14 @@ class Viewer : public mojo::ApplicationDelegate,
  private:
   // Overridden from ApplicationDelegate:
   virtual void Initialize(mojo::ApplicationImpl* app) override {
+    if (app->HasArg(kTesting)) {
+      DisplayDelegate::setDisplayDelegateCreateFunction(
+          DisplayDelegateBitmap::create);
+    } else {
+      DisplayDelegate::setDisplayDelegateCreateFunction(
+          DisplayDelegateGanesh::create);
+    }
+
     platform_impl_.reset(new PlatformImpl(app));
     blink::initialize(platform_impl_.get());
     base::i18n::InitializeICU();