Don't crash when two extension uninstall prompts are shown at the same time.

chrome/browser/extensions/api/management/management_api.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/api/management/management_api.h"
 
 #include <map>
 #include <string>
 #include <vector>
 
@@ skipping 562 matching lines @@
 }
 
 // static
 void ManagementUninstallFunctionBase::SetAutoConfirmForTest(
     bool should_proceed) {
   auto_confirm_for_test = should_proceed ? PROCEED : ABORT;
 }
 
 void ManagementUninstallFunctionBase::Finish(bool should_uninstall) {
   if (should_uninstall) {
-    bool success = service()->UninstallExtension(
-        extension_id_,
-        false, /* external uninstall */
-        NULL);
+    // The extension can be uninstalled in another window while the UI was
+    // showing. Do nothing in that case.
+    ExtensionRegistry* registry = ExtensionRegistry::Get(GetProfile());
+    const Extension* extension = registry->GetExtensionById(
+        extension_id_, ExtensionRegistry::EVERYTHING);
+    if (!extension) {
+      error_ = ErrorUtils::FormatErrorMessage(keys::kNoExtensionError,
+                                              extension_id_);
+      SendResponse(false);
+    } else {
+      bool success =
+          service()->UninstallExtension(extension_id_,
+                                        false, /* external uninstall */
+                                        NULL);
 
-    // TODO set error_ if !success
-    SendResponse(success);
+      // TODO set error_ if !success
+      SendResponse(success);
+    }
   } else {
     error_ = ErrorUtils::FormatErrorMessage(
         keys::kUninstallCanceledError, extension_id_);
     SendResponse(false);
   }
 
 }
 
 void ManagementUninstallFunctionBase::ExtensionUninstallAccepted() {
   Finish(true);
@@ skipping 214 matching lines @@
   return g_factory.Pointer();
 }
 
 void ManagementAPI::OnListenerAdded(const EventListenerInfo& details) {
   management_event_router_.reset(
       new ManagementEventRouter(Profile::FromBrowserContext(browser_context_)));
   EventRouter::Get(browser_context_)->UnregisterObserver(this);
 }
 
 }  // namespace extensions