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

ppapi/proxy/plugin_var_tracker_unittest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ipc/ipc_test_sink.h"
 #include "ppapi/proxy/plugin_var_tracker.h"
 #include "ppapi/proxy/ppapi_messages.h"
 #include "ppapi/proxy/ppapi_proxy_test.h"
 
 namespace pp {
@@ skipping 40 matching lines @@
 TEST_F(PluginVarTrackerTest, Strings) {
   std::string str("Hello");
   PluginVarTracker::VarID str_id1 = var_tracker().MakeString(str);
   EXPECT_NE(0, str_id1);
 
   PluginVarTracker::VarID str_id2 = var_tracker().MakeString(
       str.c_str(), static_cast<uint32_t>(str.size()));
   EXPECT_NE(0, str_id2);
 
   // Make sure the strings come out the other end.
-  std::string result = var_tracker().GetString(MakeString(str_id1));
-  EXPECT_EQ(str, result);
-  result = var_tracker().GetString(MakeString(str_id2));
-  EXPECT_EQ(str, result);
+  const std::string* result =
+      var_tracker().GetExistingString(MakeString(str_id1));
+  EXPECT_EQ(str, *result);
+  result = var_tracker().GetExistingString(MakeString(str_id2));
+  EXPECT_EQ(str, *result);
 }
 
 TEST_F(PluginVarTrackerTest, GetHostObject) {
   PP_Var host_object = MakeObject(12345);
 
   // Round-trip through the tracker to make sure the host object comes out the
   // other end.
   PP_Var plugin_object = var_tracker().ReceiveObjectPassRef(
       host_object, plugin_dispatcher());
   PP_Var host_object2 = var_tracker().GetHostObject(plugin_object);
@@ skipping 104 matching lines @@
   var_tracker().StopTrackingObjectWithNoReference(plugin_var);
   EXPECT_EQ(1,
             var_tracker().GetTrackedWithNoReferenceCountForObject(plugin_var));
   var_tracker().StopTrackingObjectWithNoReference(plugin_var);
   EXPECT_EQ(-1,
             var_tracker().GetTrackedWithNoReferenceCountForObject(plugin_var));
 }
 
 }  // namespace proxy
 }  // namespace pp