Fix rare crash in WebstoreInlineInstaller::CheckInlineInstallPermitted.

chrome/browser/extensions/webstore_inline_installer.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 "chrome/browser/extensions/webstore_inline_installer.h"
 
 #include <utility>
 
 #include "base/json/json_writer.h"
 #include "base/strings/stringprintf.h"
@@ skipping 120 matching lines @@
       base::JSONWriter::Write(dictionary, &json);
       return json;
     }
   }
 
   return std::string();
 }
 
 bool WebstoreInlineInstaller::CheckRequestorAlive() const {
   // The frame or tab may have gone away - cancel installation in that case.
-  return host_ != nullptr && web_contents() != nullptr;
+  return host_ != nullptr && web_contents() != nullptr &&
+         chrome::FindBrowserWithWebContents(web_contents()) != nullptr;
 }
 
 const GURL& WebstoreInlineInstaller::GetRequestorURL() const {
   return requestor_url_;
 }
 
 std::unique_ptr<ExtensionInstallPrompt::Prompt>
 WebstoreInlineInstaller::CreateInstallPrompt() const {
   std::unique_ptr<ExtensionInstallPrompt::Prompt> prompt(
       new ExtensionInstallPrompt::Prompt(
@@ skipping 134 matching lines @@
     DLOG(WARNING) << "Could not parse " << verified_site_pattern_spec <<
         " as URL pattern " << parse_result;
     return false;
   }
   verified_site_pattern.SetScheme("*");
 
   return verified_site_pattern.MatchesURL(requestor_url);
 }
 
 }  // namespace extensions