Use int for fgetc() result in headless_shell

headless/app/headless_shell.cc

 // Copyright 2016 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 <memory>
 #include <sstream>
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 261 matching lines @@
     }
     Shutdown();
   }
 
   void InputExpression() {
     // Note that a real system should read user input asynchronously, because
     // otherwise all other browser activity is suspended (e.g., page loading).
     printf(">>> ");
     std::stringstream expression;
     while (true) {
-      char c = fgetc(stdin);
+      int c = fgetc(stdin);
       if (c == EOF || c == '\n') {
         break;
       }
       expression << c;
     }
     if (expression.str() == "quit") {
       Shutdown();
       return;
     }
     devtools_client_->GetRuntime()->Evaluate(
@@ skipping 177 matching lines @@
     }
     builder.SetWindowSize(parsed_window_size);
   }
 
   return HeadlessBrowserMain(
       builder.Build(),
       base::Bind(&HeadlessShell::OnStart, base::Unretained(&shell)));
 }
 
 }  // namespace headless