Update from https://crrev.com/305340

net/base/file_stream_context_win.cc

 // Copyright (c) 2012 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 "net/base/file_stream_context.h"
 
 #include <windows.h>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 50 matching lines @@
 
 int FileStream::Context::Read(IOBuffer* buf,
                               int buf_len,
                               const CompletionCallback& callback) {
   DCHECK(!async_in_progress_);
 
   DWORD bytes_read;
   if (!ReadFile(file_.GetPlatformFile(), buf->data(), buf_len,
                 &bytes_read, &io_context_.overlapped)) {
     IOResult error = IOResult::FromOSError(GetLastError());
-    if (error.os_error == ERROR_IO_PENDING) {
+    if (error.os_error == ERROR_HANDLE_EOF)
+      return 0;  // Report EOF by returning 0 bytes read.
+    if (error.os_error == ERROR_IO_PENDING)
       IOCompletionIsPending(callback, buf);
-    } else if (error.os_error == ERROR_HANDLE_EOF) {
-      return 0;  // Report EOF by returning 0 bytes read.
-    } else {
+    else
       LOG(WARNING) << "ReadFile failed: " << error.os_error;
-    }
-    return error.result;
+    return static_cast<int>(error.result);
   }
 
   IOCompletionIsPending(callback, buf);
   return ERR_IO_PENDING;
 }
 
 int FileStream::Context::Write(IOBuffer* buf,
                                int buf_len,
                                const CompletionCallback& callback) {
   DWORD bytes_written = 0;
   if (!WriteFile(file_.GetPlatformFile(), buf->data(), buf_len,
                  &bytes_written, &io_context_.overlapped)) {
     IOResult error = IOResult::FromOSError(GetLastError());
-    if (error.os_error == ERROR_IO_PENDING) {
+    if (error.os_error == ERROR_IO_PENDING)
       IOCompletionIsPending(callback, buf);
-    } else {
+    else
       LOG(WARNING) << "WriteFile failed: " << error.os_error;
-    }
-    return error.result;
+    return static_cast<int>(error.result);
   }
 
   IOCompletionIsPending(callback, buf);
   return ERR_IO_PENDING;
 }
 
 FileStream::Context::IOResult FileStream::Context::SeekFileImpl(
     base::File::Whence whence,
     int64 offset) {
   LARGE_INTEGER result;
@@ skipping 34 matching lines @@
     in_flight_buf_ = NULL;
     CloseAndDelete();
     return;
   }
 
   int result;
   if (error == ERROR_HANDLE_EOF) {
     result = 0;
   } else if (error) {
     IOResult error_result = IOResult::FromOSError(error);
-    result = error_result.result;
+    result = static_cast<int>(error_result.result);
   } else {
     result = bytes_read;
     IncrementOffset(&io_context_.overlapped, bytes_read);
   }
 
   CompletionCallback temp_callback = callback_;
   callback_.Reset();
   scoped_refptr<IOBuffer> temp_buf = in_flight_buf_;
   in_flight_buf_ = NULL;
   temp_callback.Run(result);
 }
 
 }  // namespace net