[Sync] Add type conversion constructor for WeakHandle

chrome/browser/sync/notifier/chrome_invalidation_client_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 <string>
 
 #include "base/message_loop.h"
 #include "chrome/browser/sync/notifier/chrome_invalidation_client.h"
 #include "chrome/browser/sync/notifier/state_writer.h"
 #include "chrome/browser/sync/syncable/model_type.h"
@@ skipping 57 matching lines @@
   }
 };
 
 }  // namespace
 
 class ChromeInvalidationClientTest : public testing::Test {
  protected:
   virtual void SetUp() {
     client_.Start(kClientId, kClientInfo, kState,
                   InvalidationVersionMap(),
-                  browser_sync::WeakHandle<InvalidationVersionTracker>(
+                  browser_sync::MakeWeakHandle(
                       mock_invalidation_version_tracker_.AsWeakPtr()),
                   &mock_listener_, &mock_state_writer_,
                   fake_base_task_.AsWeakPtr());
   }
 
   virtual void TearDown() {
     client_.Stop();
     message_loop_.RunAllPending();
   }
 
@@ skipping 194 matching lines @@
   // Registered types should be preserved across Stop/Start.
   TearDown();
   SetUp();
   EXPECT_CALL(mock_listener_, OnInvalidate(MakeMapFromSet(types, "")));
   FireInvalidateAll();
 }
 
 // TODO(akalin): Flesh out unit tests.
 
 }  // namespace sync_notifier