Enable size_t to int truncation warnings in PPAPI

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 571210e9529289b1ce9865b5c44ed6f44a16d9ce..644e79e4311f515572d05b15c3334a9084659b7d 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.cc
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.cc
@@ -4,6 +4,7 @@
 
 #include "ppapi/proxy/ppapi_command_buffer_proxy.h"
 
+#include "base/numerics/safe_conversions.h"
 #include "ppapi/proxy/ppapi_messages.h"
 #include "ppapi/proxy/proxy_channel.h"
 #include "ppapi/shared_impl/api_id.h"
@@ -122,7 +123,8 @@ scoped_refptr<gpu::Buffer> PpapiCommandBufferProxy::CreateTransferBuffer(
   ppapi::proxy::SerializedHandle handle(
       ppapi::proxy::SerializedHandle::SHARED_MEMORY);
   if (!Send(new PpapiHostMsg_PPBGraphics3D_CreateTransferBuffer(
-            ppapi::API_ID_PPB_GRAPHICS_3D, resource_, size, id, &handle))) {
+            ppapi::API_ID_PPB_GRAPHICS_3D, resource_,
+            base::checked_cast<uint32_t>(size), id, &handle))) {
     return NULL;
   }