Add FileReaderInterface. Move StringFileWriter to StringFile and

util/file/file_writer.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 #include "util/file/file_writer.h"
 
 #include <algorithm>
 
 #include <limits.h>
 
 #include "base/logging.h"
+#include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <sys/uio.h>
 #include <unistd.h>
 #include "base/posix/eintr_wrapper.h"
 #endif  // OS_POSIX
 
 namespace crashpad {
 
 #if defined(OS_POSIX)
@@ skipping 146 matching lines @@
   DCHECK(file_.is_valid());
   return weak_file_handle_file_writer_.WriteIoVec(iovecs);
 }
 
 FileOffset FileWriter::Seek(FileOffset offset, int whence) {
   DCHECK(file_.is_valid());
   return weak_file_handle_file_writer_.Seek(offset, whence);
 }
 
 }  // namespace crashpad