[remoting android] Add and build host code.

remoting/host/policy_watcher.cc

 // Copyright 2015 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.
 
 // Most of this code is copied from:
 //   src/chrome/browser/policy/asynchronous_policy_loader.{h,cc}
 
 #include "remoting/host/policy_watcher.h"
 
 #include <utility>
@@ skipping 354 matching lines @@
   CFStringRef bundle_id = CFSTR("com.google.Chrome");
   policy_loader.reset(new policy::PolicyLoaderMac(
       file_task_runner,
       policy::PolicyLoaderMac::GetManagedPolicyPath(bundle_id),
       new MacPreferences(), bundle_id));
 #elif defined(OS_POSIX) && !defined(OS_ANDROID)
   policy_loader.reset(new policy::ConfigDirPolicyLoader(
       file_task_runner,
       base::FilePath(FILE_PATH_LITERAL("/etc/opt/chrome/policies")),
       policy::POLICY_SCOPE_MACHINE));
+#elif defined(OS_ANDROID)
+  NOTIMPLEMENTED();
 #else
 #error OS that is not yet supported by PolicyWatcher code.
 #endif
 
   return PolicyWatcher::CreateFromPolicyLoader(std::move(policy_loader));
 #endif  // !(OS_CHROMEOS)
 }
 
 }  // namespace remoting