[Ext Registry] Do not try to re-watch registry if we are already watching it.

chrome/browser/extensions/external_registry_loader_win.h

Index: chrome/browser/extensions/external_registry_loader_win.h
diff --git a/chrome/browser/extensions/external_registry_loader_win.h b/chrome/browser/extensions/external_registry_loader_win.h
index e14fb864adcbb1b492f8a47d5107241f8257da95..af2bee07ca55e69af212c983d36e44f70023f905 100644
--- a/chrome/browser/extensions/external_registry_loader_win.h
+++ b/chrome/browser/extensions/external_registry_loader_win.h
@@ -17,13 +17,13 @@ class ExternalRegistryLoader : public ExternalLoader {
   ExternalRegistryLoader() {}
 
  protected:
+  ~ExternalRegistryLoader() override {}  // protected for unit test.
+
   void StartLoading() override;
 
  private:
   friend class base::RefCountedThreadSafe<ExternalLoader>;
 
-  ~ExternalRegistryLoader() override {}
-
   std::unique_ptr<base::DictionaryValue> LoadPrefsOnFileThread();
   void LoadOnFileThread();
   void CompleteLoadAndStartWatchingRegistry();
@@ -31,7 +31,12 @@ class ExternalRegistryLoader : public ExternalLoader {
   void OnRegistryKeyChanged(base::win::RegKey* key);
 
   base::win::RegKey hklm_key_;
+  // Whether or not HKLM registry watching is active.
+  bool is_watching_hklm_;
+
   base::win::RegKey hkcu_key_;
+  // Whether or not HKCU registry watching is active.
+  bool is_watching_hkcu_;
 
   DISALLOW_COPY_AND_ASSIGN(ExternalRegistryLoader);
 };