Speculative fix for crash in DOMUIThumbnailSource.

chrome/browser/dom_ui/dom_ui_favicon_source.cc

Index: chrome/browser/dom_ui/dom_ui_favicon_source.cc
diff --git a/chrome/browser/dom_ui/dom_ui_favicon_source.cc b/chrome/browser/dom_ui/dom_ui_favicon_source.cc
index f80aa70b4130a844c91bc43ebb02a7c5fa73e47c..d6585034ea6bdafeb0df3f45ad876eb17631fb29 100644
--- a/chrome/browser/dom_ui/dom_ui_favicon_source.cc
+++ b/chrome/browser/dom_ui/dom_ui_favicon_source.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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.
 
@@ -6,6 +6,7 @@
 
 #include "app/resource_bundle.h"
 #include "base/callback.h"
+#include "chrome/browser/chrome_thread.h"
 #include "chrome/browser/profile.h"
 #include "chrome/common/url_constants.h"
 #include "grit/app_resources.h"
@@ -15,9 +16,14 @@ DOMUIFavIconSource::DOMUIFavIconSource(Profile* profile)
       profile_(profile) {
 }
 
+DOMUIFavIconSource::~DOMUIFavIconSource() {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
+}
+
 void DOMUIFavIconSource::StartDataRequest(const std::string& path,
                                           bool is_off_the_record,
                                           int request_id) {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   FaviconService* favicon_service =
       profile_->GetFaviconService(Profile::EXPLICIT_ACCESS);
   if (favicon_service) {
@@ -40,12 +46,19 @@ void DOMUIFavIconSource::StartDataRequest(const std::string& path,
   }
 }
 
+std::string DOMUIFavIconSource::GetMimeType(const std::string&) const {
+  // We need to explicitly return a mime type, otherwise if the user tries to
+  // drag the image they get no extension.
+  return "image/png";
+}
+
 void DOMUIFavIconSource::OnFavIconDataAvailable(
     FaviconService::Handle request_handle,
     bool know_favicon,
     scoped_refptr<RefCountedMemory> data,
     bool expired,
     GURL icon_url) {
+  DCHECK(ChromeThread::CurrentlyOn(ChromeThread::UI));
   FaviconService* favicon_service =
       profile_->GetFaviconService(Profile::EXPLICIT_ACCESS);
   int request_id = cancelable_consumer_.GetClientData(favicon_service,