Introducing gpu::CommandBufferId as a distinct, IdType<...>-based type.

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 0a7524bd58ee54bbf0b27f16fdc5f2b80d00874e..58ad59a3cb57cbbbea44b0bbd8fcdac47d253876 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -20,7 +20,7 @@ PpapiCommandBufferProxy::PpapiCommandBufferProxy(
     PluginDispatcher* dispatcher,
     const gpu::Capabilities& capabilities,
     const SerializedHandle& shared_state,
-    uint64_t command_buffer_id)
+    gpu::CommandBufferId command_buffer_id)
     : command_buffer_id_(command_buffer_id),
       capabilities_(capabilities),
       resource_(resource),
@@ -195,7 +195,7 @@ gpu::CommandBufferNamespace PpapiCommandBufferProxy::GetNamespaceID() const {
   return gpu::CommandBufferNamespace::GPU_IO;
 }
 
-uint64_t PpapiCommandBufferProxy::GetCommandBufferID() const {
+gpu::CommandBufferId PpapiCommandBufferProxy::GetCommandBufferID() const {
   return command_buffer_id_;
 }