Make RenderPass::Id an isolated class

cc/quads/render_pass_id.cc

Index: cc/quads/render_pass_id.cc
diff --git a/cc/quads/render_pass_id.cc b/cc/quads/render_pass_id.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d15240dba80f6db7a3cbdc8e9e74acf4374123c6
--- /dev/null
+++ b/cc/quads/render_pass_id.cc
@@ -0,0 +1,15 @@
+// Copyright 2014 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.
+
+#include "cc/quads/render_pass_id.h"
+
+namespace cc {
+
+void* RenderPassId::AsTracingId() const {
+  COMPILE_ASSERT(sizeof(size_t) <= sizeof(void*),  // NOLINT
+                 size_t_bigger_than_pointer);
+  return reinterpret_cast<void*>(base::HashPair(layer_id, index));
+}
+
+}  // namespace cc