Add Gr*Proxy classes

src/gpu/GrSurfaceProxy.cpp

Index: src/gpu/GrSurfaceProxy.cpp
diff --git a/src/gpu/GrSurfaceProxy.cpp b/src/gpu/GrSurfaceProxy.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e1ab54196806e71bb8e2df179f14bfc1e2207df9
--- /dev/null
+++ b/src/gpu/GrSurfaceProxy.cpp
@@ -0,0 +1,19 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrSurfaceProxy.h"
+
+#include "SkAtomics.h"
+
+uint32_t GrSurfaceProxy::CreateUniqueID() {
+    static int32_t gUniqueID = SK_InvalidUniqueID;
+    uint32_t id;
+    do {
+        id = static_cast<uint32_t>(sk_atomic_inc(&gUniqueID) + 1);
+    } while (id == SK_InvalidUniqueID);
+    return id;
+}