Fix an NPE in BrowserPluginGuest during guest teardown while showing interstitial.

content/browser/browser_plugin/browser_plugin_guest.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/browser/browser_plugin/browser_plugin_guest.h"
 
 #include <algorithm>
 
 #include "base/message_loop/message_loop.h"
 #include "base/pickle.h"
@@ skipping 478 matching lines @@
     pending_messages_.pop_front();
     SendMessageToEmbedder(message_ptr.release());
   }
 }
 
 void BrowserPluginGuest::SendTextInputTypeChangedToView(
     RenderWidgetHostViewBase* guest_rwhv) {
   if (!guest_rwhv)
     return;
 
+  if (!owner_web_contents_) {
+    // If we were showing an interstitial, then we can end up here during
+    // embedder shutdown or when the embedder navigates to a different page.
+    // The call stack is roughly:
+    // BrowserPluginGuest::SetFocus()
+    // content::InterstitialPageImpl::Hide()
+    // content::InterstitialPageImpl::DontProceed().
+    //
+    // TODO(lazyboy): Write a WebUI test once http://crbug.com/463674 is fixed.
+    return;
+  }
+
   guest_rwhv->TextInputTypeChanged(last_text_input_type_, last_input_mode_,
                                    last_can_compose_inline_, last_input_flags_);
   // Enable input method for guest if it's enabled for the embedder.
   if (!static_cast<RenderViewHostImpl*>(
            owner_web_contents_->GetRenderViewHost())->input_method_active()) {
     return;
   }
   RenderViewHostImpl* guest_rvh =
       static_cast<RenderViewHostImpl*>(GetWebContents()->GetRenderViewHost());
   guest_rvh->SetInputMethodActive(true);
@@ skipping 407 matching lines @@
 void BrowserPluginGuest::OnImeCompositionRangeChanged(
       const gfx::Range& range,
       const std::vector<gfx::Rect>& character_bounds) {
   static_cast<RenderWidgetHostViewBase*>(
       web_contents()->GetRenderWidgetHostView())->ImeCompositionRangeChanged(
           range, character_bounds);
 }
 #endif
 
 }  // namespace content