base: Add SetEnv() to EnvVarGetter class and get rid of the some ifdefs.

net/proxy/proxy_config_service_linux_unittest.cc

 // Copyright (c) 2010 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/proxy_config_service_linux.h"
 
 #include <map>
 #include <string>
 #include <vector>
 
@@ skipping 96 matching lines @@
   virtual bool GetEnv(const char* variable_name, std::string* result) {
     const char* env_value = table.Get(variable_name);
     if (env_value) {
       // Note that the variable may be defined but empty.
       *result = env_value;
       return true;
     }
     return false;
   }
 
+  virtual void SetEnv(const char* variable_name, const std::string& new_value) {
+    NOTIMPLEMENTED();
+  }
   // Intentionally public, for convenience when setting up a test.
   EnvVarValues values;
 
  private:
   SettingsTable<const char*> table;
 };
 
 class MockGConfSettingGetter
     : public ProxyConfigServiceLinux::GConfSettingGetter {
  public:
@@ skipping 1239 matching lines @@
         new ProxyConfigServiceLinux(env_getter));
     ProxyConfig config;
     sync_config_getter.SetupAndInitialFetch();
     sync_config_getter.SyncGetProxyConfig(&config);
     EXPECT_TRUE(config.auto_detect());
     EXPECT_EQ(GURL(), config.pac_url());
   }
 }
 
 }  // namespace net