Add signalSyncPoint to the WebGraphicsContext3D command buffer impls.

cc/resources/sync_point_helper.h

Index: cc/resources/sync_point_helper.h
diff --git a/cc/resources/sync_point_helper.h b/cc/resources/sync_point_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..c42fb1113466b8e518920c3d6ca5f68a91ca2e72
--- /dev/null
+++ b/cc/resources/sync_point_helper.h
@@ -0,0 +1,43 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_RESOURCES_SYNC_POINT_HELPER_H_
+#define CC_RESOURCES_SYNC_POINT_HELPER_H_
+
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace WebKit { class WebGraphicsContext3D; }
+
+namespace cc {
+class SignalSyncPointCallbackClass;
+
+class CC_EXPORT SyncPointHelper {
+ public:
+  // Requests a callback to |closure| when the |sync_point| is reached by the
+  // |context3d|. If the SyncPointHelper* returned is destroyed, the callback
+  // request will be aborted.
+  //
+  // The returned pointer must be kept alive until either |closure| is called or
+  // the |context3d| is destroyed.

[piman, 2013/04/26 01:20:52]

Could we make WGC3D::signalSyncPoint take ownership of it instead (sticking it
into the SignalSyncPointCallback)? That way there's no way to get it wrong.

[danakj, 2013/04/26 01:39:30]

That was my original plan but if the context is destroyed and never calls it
then you like the object instance and that seems crappy. To avoid that wed need
the context to call all pending signals when its destroyed, I think. 

+  static scoped_ptr<SyncPointHelper> SignalSyncPoint(
+      WebKit::WebGraphicsContext3D* context3d,
+      unsigned sync_point,
+      const base::Closure& closure);
+
+  ~SyncPointHelper();
+
+ private:
+  SyncPointHelper(scoped_ptr<SignalSyncPointCallbackClass> callback_class);
+
+  scoped_ptr<SignalSyncPointCallbackClass> callback_class_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncPointHelper);
+};
+
+}  // namespace cc
+
+#endif  //  CC_RESOURCES_SYNC_POINT_HELPER_H_