devtools_protocol.cc: fix ptr to bool conversion warning

chrome/browser/devtools/devtools_protocol.cc

 // Copyright (c) 2013 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/devtools/devtools_protocol.h"
 
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/strings/stringprintf.h"
 
@@ skipping 99 matching lines @@
 
   return true;
 }
 
 // static
 bool DevToolsProtocol::ParseResponse(const std::string& json,
                                      int* command_id,
                                      int* error_code) {
   scoped_ptr<base::Value> value(base::JSONReader::Read(json));
   if (!value || !value->IsType(base::Value::TYPE_DICTIONARY))
-    return nullptr;
+    return false;
 
   scoped_ptr<base::DictionaryValue> dict(
       static_cast<base::DictionaryValue*>(value.release()));
 
   if (!dict->GetInteger(kIdParam, command_id))
-    return nullptr;
+    return false;
 
   *error_code = 0;
   base::DictionaryValue* error_dict = nullptr;
   if (dict->GetDictionary(kErrorParam, &error_dict))
     error_dict->GetInteger(kErrorCodeParam, error_code);
   return true;
 }