Enable size_t to int truncation warnings in PPAPI

ppapi/proxy/serialized_var_unittest.cc

 // Copyright (c) 2012 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 "ppapi/proxy/ppapi_proxy_test.h"
 
 #include "ppapi/proxy/proxy_object_var.h"
 #include "ppapi/proxy/serialized_var.h"
 #include "ppapi/shared_impl/proxy_lock.h"
 
@@ skipping 240 matching lines @@
     // ReceiveInputs keep the "track_with_no_reference_count" alive until
     // they're destroyed.
     var_tracker().AddRefVar(plugin_objects[0]);
     EXPECT_EQ(1, var_tracker().GetRefCountForObject(plugin_objects[0]));
     var_tracker().ReleaseVar(plugin_objects[0]);
     EXPECT_EQ(0, var_tracker().GetRefCountForObject(plugin_objects[0]));
     EXPECT_EQ(2u, sink().message_count());
 
     // Take a reference to a string and then release it. Make sure no messages
     // are sent.
-    uint32_t old_message_count = sink().message_count();
+    uint32_t old_message_count = static_cast<uint32_t>(sink().message_count());
     var_tracker().AddRefVar(plugin_objects[1]);
     EXPECT_EQ(2, var_tracker().GetRefCountForObject(plugin_objects[1]));
     var_tracker().ReleaseVar(plugin_objects[1]);
     EXPECT_EQ(1, var_tracker().GetRefCountForObject(plugin_objects[1]));
     EXPECT_EQ(old_message_count, sink().message_count());
   }
 
   // Since we didn't keep any refs to the objects or strings, so they should
   // have been freed.
   EXPECT_EQ(-1, var_tracker().GetRefCountForObject(plugin_objects[0]));
@@ skipping 106 matching lines @@
   }
 
   // When the ReturnValue object goes out of scope, it should have sent a
   // release message to the browser.
   EXPECT_EQ(-1, var_tracker().GetRefCountForObject(plugin_object));
   EXPECT_EQ(1u, sink().message_count());
 }
 
 }  // namespace proxy
 }  // namespace ppapi