Fix some types at the IPC layer. Sizes should be unsigned.

ppapi/proxy/ppb_video_decoder_proxy.cc

Index: ppapi/proxy/ppb_video_decoder_proxy.cc
===================================================================
--- ppapi/proxy/ppb_video_decoder_proxy.cc	(revision 171343)
+++ ppapi/proxy/ppb_video_decoder_proxy.cc	(working copy)
@@ -226,7 +226,7 @@
 
 void PPB_VideoDecoder_Proxy::OnMsgDecode(
     const HostResource& decoder,
-    const HostResource& buffer, int32 id, int32 size) {
+    const HostResource& buffer, int32 id, uint32 size) {
   EnterHostFromHostResourceForceCallback<PPB_VideoDecoder_API> enter(
       decoder, callback_factory_,
       &PPB_VideoDecoder_Proxy::SendMsgEndOfBitstreamACKToPlugin, decoder, id);