Proxy PPB_Var, fix o-o-p string var id tracking.

ppapi/proxy/plugin_var_serialization_rules.cc

Index: ppapi/proxy/plugin_var_serialization_rules.cc
diff --git a/ppapi/proxy/plugin_var_serialization_rules.cc b/ppapi/proxy/plugin_var_serialization_rules.cc
index a3d82312de6de19fd02b099827e8a308133c6d55..8ba557462869b5aad7c3306c2683bd06d405824e 100644
--- a/ppapi/proxy/plugin_var_serialization_rules.cc
+++ b/ppapi/proxy/plugin_var_serialization_rules.cc
@@ -24,10 +24,14 @@ PP_Var PluginVarSerializationRules::SendCallerOwned(const PP_Var& var,
   if (var.type == PP_VARTYPE_OBJECT)
     return var_tracker_->GetHostObject(var);
 
-  // Nothing to do since we manage the refcount, other than retrieve the string
-  // to use for IPC.
-  if (var.type == PP_VARTYPE_STRING)
-    *str_val = var_tracker_->GetString(var);
+  // Retrieve the string to use for IPC.
+  if (var.type == PP_VARTYPE_STRING) {
+    const std::string* var_string = var_tracker_->GetExistingString(var);
+    if (var_string)
+      *str_val = *var_string;
+    else
+      NOTREACHED() << "Trying to send unknown string over IPC.";
+  }
   return var;
 }
 
@@ -119,8 +123,13 @@ PP_Var PluginVarSerializationRules::BeginSendPassRef(const PP_Var& var,
   if (var.type == PP_VARTYPE_OBJECT)
     return var_tracker_->GetHostObject(var);
 
-  if (var.type == PP_VARTYPE_STRING)
-    *str_val = var_tracker_->GetString(var);
+  if (var.type == PP_VARTYPE_STRING) {
+    const std::string* var_string = var_tracker_->GetExistingString(var);
+    if (var_string)
+      *str_val = *var_string;
+    else
+      NOTREACHED() << "Trying to send unknown string over IPC.";
+  }
   return var;
 }