[DevTools] Address crash by checking if Tab loaded successfully

chrome/browser/android/dev_tools_manager_delegate_android.cc

 // Copyright 2014 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 "chrome/browser/android/dev_tools_manager_delegate_android.h"
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 122 matching lines @@
     int index;
     if (!FindTab(&model, &index))
       return NULL;
     WebContents* web_contents = model->GetWebContentsAt(index);
     if (!web_contents) {
       // The tab has been pushed out of memory, pull it back.
       TabAndroid* tab = model->GetTabAt(index);
       if (!tab)
         return NULL;
 
-      tab->LoadIfNeeded();
+      if (!tab->LoadIfNeeded())
+        return NULL;
+
       web_contents = model->GetWebContentsAt(index);
       if (!web_contents)
         return NULL;
     }
     return DevToolsAgentHost::GetOrCreateFor(web_contents);
   }
 
   virtual bool Activate() const OVERRIDE {
     TabModel* model;
     int index;
@@ skipping 182 matching lines @@
     const GURL& url) {
   Profile* profile = ProfileManager::GetLastUsedProfile()->GetOriginalProfile();
   history::TopSites* top_sites = profile->GetTopSites();
   if (top_sites) {
     scoped_refptr<base::RefCountedMemory> data;
     if (top_sites->GetPageThumbnail(url, false, &data))
       return std::string(data->front_as<char>(), data->size());
   }
   return std::string();
 }