Enable compiling GN by default.

tools/gn/input_file_manager.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 "tools/gn/input_file_manager.h"
 
 #include "base/bind.h"
 #include "base/stl_util.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/parser.h"
@@ skipping 147 matching lines @@
   // The other load could have failed. In this case that error will be printed
   // to the console, but we need to return something here, so make up a
   // dummy error.
   if (!data->parsed_root)
     *err = Err(origin, "File parse failed");
   return data->parsed_root.get();
 }
 
 int InputFileManager::GetInputFileCount() const {
   base::AutoLock lock(lock_);
-  return input_files_.size();
+  return static_cast<int>(input_files_.size());
 }
 
 void InputFileManager::GetAllPhysicalInputFileNames(
     std::vector<base::FilePath>* result) const {
   base::AutoLock lock(lock_);
   result->reserve(input_files_.size());
   for (InputFileMap::const_iterator i = input_files_.begin();
        i != input_files_.end(); ++i) {
     if (!i->second->file.physical_name().empty())
       result->push_back(i->second->file.physical_name());
@@ skipping 88 matching lines @@
     callbacks.swap(data->scheduled_callbacks);
   }
 
   // Run pending invocations. Theoretically we could schedule each of these
   // separately to get some parallelism. But normally there will only be one
   // item in the list, so that's extra overhead and complexity for no gain.
   for (size_t i = 0; i < callbacks.size(); i++)
     callbacks[i].Run(unowned_root);
   return true;
 }