Make mojo::Callback<>::Runnable::Run non-const.

chrome/browser/chromeos/arc/arc_policy_bridge_unittest.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 "base/macros.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/arc/arc_policy_bridge.h"
 #include "components/arc/test/fake_arc_bridge_service.h"
@@ skipping 23 matching lines @@
                     policy::POLICY_DOMAIN_CHROME, std::string())))
         .WillRepeatedly(ReturnRef(policy_map_));
   }
 
  protected:
   class PolicyStringRunnable
       : public ArcPolicyBridge::GetPoliciesCallback::Runnable {
    public:
     explicit PolicyStringRunnable(mojo::String expected)
         : expected_(expected) {}
-    void Run(const mojo::String& policies) const override {
+    void Run(const mojo::String& policies) override {
       EXPECT_EQ(expected_, policies);
     }
 
    private:
     mojo::String expected_;
   };
 
   class PolicyStringCallback : public ArcPolicyBridge::GetPoliciesCallback {
    public:
     explicit PolicyStringCallback(mojo::String expected)
@@ skipping 25 matching lines @@
       policy::POLICY_SCOPE_USER, policy::POLICY_SOURCE_CLOUD,
       new base::StringValue("{\"application\": \"com.android.chrome\"}"),
       nullptr);
   PolicyStringCallback chrome_callback(
       "{\"ArcApplicationPolicy\":"
       "\"{\\\"application\\\": \\\"com.android.chrome\\\"}\"}");
   policy_bridge()->GetPolicies(chrome_callback);
 }
 
 }  // namespace arc