Add method GetKeyFromSystem to WiFiService on Windows and Mac.

components/wifi/fake_wifi_service.cc

Index: components/wifi/fake_wifi_service.cc
diff --git a/components/wifi/fake_wifi_service.cc b/components/wifi/fake_wifi_service.cc
index 28911d2f7a7c463b5e688d34fc37655d994de7a0..ea0e87256a0e9f6d67e765a894bcb440d3f3eedb 100644
--- a/components/wifi/fake_wifi_service.cc
+++ b/components/wifi/fake_wifi_service.cc
@@ -254,6 +254,12 @@ class FakeWiFiService : public WiFiService {
     }
   }
 
+  virtual void GetKeyFromSystem(const std::string& network_guid,
+                                std::string* key_data,
+                                std::string* error) OVERRIDE {
+    *error = "not-found";
+  }
+
   virtual void SetEventObservers(
       scoped_refptr<base::MessageLoopProxy> message_loop_proxy,
       const NetworkGuidListCallback& networks_changed_observer,