[Android] Fix gn build for instrumentation tests.

tools/android/forwarder2/device_forwarder_main.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 <signal.h>
 #include <stdlib.h>
 
 #include <iostream>
 #include <string>
 
@@ skipping 106 matching lines @@
   ClientDelegate() : has_failed_(false) {}
 
   bool has_failed() const { return has_failed_; }
 
   // Daemon::ClientDelegate:
   virtual void OnDaemonReady(Socket* daemon_socket) override {
     char buf[kBufSize];
     const int bytes_read = daemon_socket->Read(
         buf, sizeof(buf) - 1 /* leave space for null terminator */);
     CHECK_GT(bytes_read, 0);
-    DCHECK(bytes_read < sizeof(buf));
+    DCHECK(static_cast<unsigned int>(bytes_read) < sizeof(buf));
     buf[bytes_read] = 0;
     base::StringPiece msg(buf, bytes_read);
     if (msg.starts_with("ERROR")) {
       LOG(ERROR) << msg;
       has_failed_ = true;
       return;
     }
   }
 
  private:
@@ skipping 22 matching lines @@
     return 1;
   return client_delegate.has_failed();
 }
 
 }  // namespace
 }  // namespace forwarder2
 
 int main(int argc, char** argv) {
   return forwarder2::RunDeviceForwarder(argc, argv);
 }