Use std::string instead of mojo::String in //net.

net/proxy/mojo_proxy_resolver_v8_tracing_bindings_unittest.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.
 
 #include "net/proxy/mojo_proxy_resolver_v8_tracing_bindings.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace net {
 
 class MojoProxyResolverV8TracingBindingsTest : public testing::Test {
  public:
   MojoProxyResolverV8TracingBindingsTest() = default;
 
   void SetUp() override {
     bindings_.reset(new MojoProxyResolverV8TracingBindings<
                     MojoProxyResolverV8TracingBindingsTest>(this));
   }
 
-  void Alert(const mojo::String& message) {
-    alerts_.push_back(message.To<std::string>());
-  }
+  void Alert(const std::string& message) { alerts_.push_back(message); }
 
-  void OnError(int32_t line_number, const mojo::String& message) {
-    errors_.push_back(std::make_pair(line_number, message.To<std::string>()));
+  void OnError(int32_t line_number, const std::string& message) {
+    errors_.push_back(std::make_pair(line_number, message));
   }
 
   void ResolveDns(std::unique_ptr<HostResolver::RequestInfo> request_info,
                   interfaces::HostResolverRequestClientPtr client) {}
 
  protected:
   std::unique_ptr<MojoProxyResolverV8TracingBindings<
       MojoProxyResolverV8TracingBindingsTest>>
       bindings_;
 
@@ skipping 12 matching lines @@
   EXPECT_FALSE(bindings_->GetNetLogWithSource().net_log());
 
   ASSERT_EQ(1u, alerts_.size());
   EXPECT_EQ("alert", alerts_[0]);
   ASSERT_EQ(1u, errors_.size());
   EXPECT_EQ(-1, errors_[0].first);
   EXPECT_EQ("error", errors_[0].second);
 }
 
 }  // namespace net