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

ppapi/proxy/serialized_var.h

Index: ppapi/proxy/serialized_var.h
diff --git a/ppapi/proxy/serialized_var.h b/ppapi/proxy/serialized_var.h
index 98cafa0dac3afe009b54e821ec53dbaa063fa768..ab7fd3e88a5b7e846bc498d3da287e2cfc8f9e3b 100644
--- a/ppapi/proxy/serialized_var.h
+++ b/ppapi/proxy/serialized_var.h
@@ -84,6 +84,10 @@ class PPAPI_PROXY_EXPORT SerializedVar {
     return inner_->ReadFromMessage(m, iter);
   }
 
+  bool is_valid_var() const {
+    return inner_->is_valid_var();
+  }
+
   RawVarDataGraph* raw_var_data() const {
     return inner_->raw_var_data();
   }
@@ -110,6 +114,10 @@ class PPAPI_PROXY_EXPORT SerializedVar {
       serialization_rules_ = serialization_rules;
     }
 
+    bool is_valid_var() const {
+      return is_valid_var_;
+    }
+
     RawVarDataGraph* raw_var_data() {
       return raw_var_data_.get();
     }
@@ -162,6 +170,9 @@ class PPAPI_PROXY_EXPORT SerializedVar {
 
     CleanupMode cleanup_mode_;
 
+    // If the var is not properly serialized, this will be false.
+    bool is_valid_var_;
+
 #ifndef NDEBUG
     // When being sent or received over IPC, we should only be serialized or
     // deserialized once. These flags help us assert this is true.
@@ -342,6 +353,7 @@ class PPAPI_PROXY_EXPORT SerializedVarReceiveInput {
 
   PP_Var Get(Dispatcher* dispatcher);
   PP_Var GetForInstance(Dispatcher* dispatcher, PP_Instance instance);
+  bool is_valid_var() { return serialized_.is_valid_var(); }
 
  private:
   const SerializedVar& serialized_;