Fix a few warnings that -Wnull-conversion of a future clang will complain about.

content/renderer/render_view_impl.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 "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 #include <string>
 #include <vector>
@@ skipping 4914 matching lines @@
 void RenderViewImpl::StartPluginIme() {
   IPC::Message* msg = new ViewHostMsg_StartPluginIme(routing_id());
   // This message can be sent during event-handling, and needs to be delivered
   // within that context.
   msg->set_unblock(true);
   Send(msg);
 }
 
 gfx::PluginWindowHandle RenderViewImpl::AllocateFakePluginWindowHandle(
     bool opaque, bool root) {
-  gfx::PluginWindowHandle window = NULL;
+  gfx::PluginWindowHandle window = gfx::kNullPluginWindow;
   Send(new ViewHostMsg_AllocateFakePluginWindowHandle(
       routing_id(), opaque, root, &window));
   if (window) {
     fake_plugin_window_handles_.insert(window);
   }
   return window;
 }
 
 void RenderViewImpl::DestroyFakePluginWindowHandle(
     gfx::PluginWindowHandle window) {
@@ skipping 255 matching lines @@
 bool RenderViewImpl::WebWidgetHandlesCompositorScheduling() const {
   return !!RenderThreadImpl::current()->compositor_thread();
 }
 
 void RenderViewImpl::OnJavaBridgeInit() {
   DCHECK(!java_bridge_dispatcher_.get());
 #if defined(ENABLE_JAVA_BRIDGE)
   java_bridge_dispatcher_.reset(new JavaBridgeDispatcher(this));
 #endif
 }