Don't send PP_Vars/V8 values with cycles across PostMessage

ppapi/proxy/serialized_var.cc

Index: ppapi/proxy/serialized_var.cc
diff --git a/ppapi/proxy/serialized_var.cc b/ppapi/proxy/serialized_var.cc
index 1217a83ba5cf6b645257a02e11f29fa0c7d74e3a..2642ecf4c171356af1f783ad31c28622a905edcb 100644
--- a/ppapi/proxy/serialized_var.cc
+++ b/ppapi/proxy/serialized_var.cc
@@ -15,6 +15,11 @@
 #include "ppapi/shared_impl/var.h"
 #include "ppapi/thunk/enter.h"
 
+namespace {
+const char kSerializationError[] = "Failed to serialize a PP_Var. It may have "
+    "cycles or be of an unsupported type: ";
+}  // namespace
+
 namespace ppapi {
 namespace proxy {
 
@@ -107,7 +112,21 @@ void SerializedVar::Inner::WriteToMessage(IPC::Message* m) const {
   DCHECK(!has_been_serialized_);
   has_been_serialized_ = true;
 #endif
-  RawVarDataGraph::Create(var_, instance_)->Write(m);
+  scoped_ptr<RawVarDataGraph> data =
+      RawVarDataGraph::Create(var_, instance_, false);
+  if (data) {
+    data->Write(m);
+  } else {
+    // TODO(raymes): It's not ideal to log here. We should probably propagate
+    // the error all the way through to the location at which the var is used.
+    // However, SerializedVar isn't set up to propagate errors well. This case
+    // should only occur if the the PP_Var passed in is somehow corrupt or a var
+    // with reference cycles is passed in.
+    PpapiGlobals::Get()->LogWithSource(
+        instance_, PP_LOGLEVEL_ERROR, std::string(),
+        kSerializationError + ppapi::Var::PPVarToLogString(var_));

[dmichael (off chromium), 2013/06/04 16:59:10]

Yeah...  this is going to result in sending a message while inside the
serialization for another message. It probably works fine, but it seems like
something we ought to try to avoid.

I wonder if we could make an invalid form of a serialized Var, so that the
recipient will receive the invalid Var, know something went wrong, and can take
appropriate action there (log and don't send a message, in the case of
Messaging). [This would be purely an implementation detail; we wouldn't expose
the invalid kind of var to plugins]

[raymes, 2013/06/04 19:36:06]

I actually went down this road first and then backtracked on it because it felt
a bit nasty as well :P But I do prefer it. I've changed it to do that.

+    RawVarDataGraph::Create(PP_MakeUndefined(), instance_, false)->Write(m);
+  }
 }
 
 bool SerializedVar::Inner::ReadFromMessage(const IPC::Message* m,