Added an extra sync token field for extra command buffer identification.

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 f999b733a43cc27b8e53cc3cde4acd8f2591c3ed..d36b5d485c01d04f461f7ea96857ce13c3753047 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -213,6 +213,10 @@ bool PpapiCommandBufferProxy::CanWaitUnverifiedSyncToken(
   return false;
 }
 
+uint32_t PpapiCommandBufferProxy::GetExtraCommandBufferData() const {
+  return 0;
+}
+
 uint32 PpapiCommandBufferProxy::InsertSyncPoint() {
   uint32 sync_point = 0;
   if (last_state_.error == gpu::error::kNoError) {