Add DCHECK to WebViewPlugin helper to assert WebFrameClient params.

components/plugins/renderer/webview_plugin.cc

 // Copyright 2013 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 "components/plugins/renderer/webview_plugin.h"
 
 #include <stddef.h>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 299 matching lines @@
     return;
   if (plugin_->container_) {
     // This should never happen; see also crbug.com/545039 for context.
     DCHECK(!plugin_->is_painting_);
     plugin_->container_->scheduleAnimation();
   }
 }
 
 void WebViewPlugin::WebViewHelper::didClearWindowObject(
     WebLocalFrame* frame) {
+  DCHECK_EQ(frame, web_view_->mainFrame());
   if (!plugin_->delegate_)
     return;
 
   v8::Isolate* isolate = blink::mainThreadIsolate();
   v8::HandleScope handle_scope(isolate);
   v8::Local<v8::Context> context = frame->mainWorldScriptContext();
   DCHECK(!context.IsEmpty());
 
   v8::Context::Scope context_scope(context);
   v8::Local<v8::Object> global = context->Global();
@@ skipping 16 matching lines @@
   if (!delegate_)
     return;
 
   // The delegate may instantiate a new plugin.
   delegate_->OnUnobscuredRectUpdate(gfx::Rect(unobscured_rect));
   // The delegate may have dirtied style and layout of the WebView.
   // See for example the resizePoster function in plugin_poster.html.
   // Run the lifecycle now so that it is clean.
   web_view()->updateAllLifecyclePhases();
 }