[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..3999fec6d7760a70b80193e34d7e7bef58eb5ca1 100644
--- a/chrome/browser/extensions/external_registry_loader_win.h
+++ b/chrome/browser/extensions/external_registry_loader_win.h
@@ -14,7 +14,7 @@ namespace extensions {
 
 class ExternalRegistryLoader : public ExternalLoader {
  public:
-  ExternalRegistryLoader() {}
+  ExternalRegistryLoader();
 
  protected:
   void StartLoading() override;
@@ -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);
 };