Added a unique command buffer ID for command buffers.

ppapi/proxy/ppapi_command_buffer_proxy.cc

Index: ppapi/proxy/ppapi_command_buffer_proxy.cc
diff --git a/ppapi/proxy/ppapi_command_buffer_proxy.cc b/ppapi/proxy/ppapi_command_buffer_proxy.cc
index 7a42524bff2fe2827ffbce153f9d62f1a011b108..47dc16fda84596a5a58ec84e6a2835044c2f3e48 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -13,12 +13,15 @@
 namespace ppapi {
 namespace proxy {
 
+// TODO(dyen): to support fences on Ppapi, we need to plumb the command buffer
+// id that the ppapi command buffer forwards to.
 PpapiCommandBufferProxy::PpapiCommandBufferProxy(
     const ppapi::HostResource& resource,
     PluginDispatcher* dispatcher,
     const gpu::Capabilities& capabilities,
     const SerializedHandle& shared_state)
-    : capabilities_(capabilities),
+    : CommandBuffer(gpu::kCommandBufferNamespace_Invalid, 0),
+      capabilities_(capabilities),
       resource_(resource),
       dispatcher_(dispatcher) {
   shared_state_shm_.reset(