[webkit glue] Make signedPublicKeyAndChallengeString() return an empty instead of null string.

webkit/glue/webkitplatformsupport_impl.cc

 // Copyright (c) 2011 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 "webkit/glue/webkitplatformsupport_impl.h"
 
 #if defined(OS_LINUX)
 #include <malloc.h>
 #endif
 
@@ skipping 577 matching lines @@
 
 long long WebKitPlatformSupportImpl::databaseGetSpaceAvailableForOrigin(
     const WebKit::WebString& origin_identifier) {
   return 0;
 }
 
 WebKit::WebString WebKitPlatformSupportImpl::signedPublicKeyAndChallengeString(
     unsigned key_size_index,
     const WebKit::WebString& challenge,
     const WebKit::WebURL& url) {
-  NOTREACHED();
-  return WebKit::WebString();
+  return WebKit::WebString("");
 }
 
 #if defined(OS_LINUX)
 static size_t memoryUsageMBLinux() {
   struct mallinfo minfo = mallinfo();
   uint64_t mem_usage =
 #if defined(USE_TCMALLOC)
       minfo.uordblks
 #else
       (minfo.hblkhd + minfo.arena)
@@ skipping 69 matching lines @@
 }
 
 // static
 void WebKitPlatformSupportImpl::DestroyCurrentThread(void* thread) {
   WebThreadImplForMessageLoop* impl =
       static_cast<WebThreadImplForMessageLoop*>(thread);
   delete impl;
 }
 
 }  // namespace webkit_glue