Clean up threading model of external extension providers

chrome/browser/extensions/external_extension_provider.h

Index: chrome/browser/extensions/external_extension_provider.h
diff --git a/chrome/browser/extensions/external_extension_provider.h b/chrome/browser/extensions/external_extension_provider.h
index 5bcce1d5f4d7d150d3b50304038a204900330f5c..8b4d7f288b2fca3e9f5fba1f375140b92ba71503 100644
--- a/chrome/browser/extensions/external_extension_provider.h
+++ b/chrome/browser/extensions/external_extension_provider.h
@@ -6,6 +6,9 @@
 #define CHROME_BROWSER_EXTENSIONS_EXTERNAL_EXTENSION_PROVIDER_H_
 #pragma once
 
+#include <vector>
+
+#include "base/linked_ptr.h"
 #include "chrome/common/extensions/extension.h"
 
 class FilePath;
@@ -32,16 +35,23 @@ class ExternalExtensionProvider {
          const GURL& update_url,
          Extension::Location location) = 0;
 
+     // Called after all the external extensions have been reported through
+     // the above two methods.
+     virtual void OnExternalProviderReady() = 0;
+
    protected:
      virtual ~Visitor() {}
   };
 
   virtual ~ExternalExtensionProvider() {}
 
-  // Enumerate registered extension, calling OnExternalExtensionFound on
-  // the |visitor| object for each registered extension found. |ids_to_ignore|
-  // contains a list of extension ids that should not result in a call back.
-  virtual void VisitRegisteredExtension(Visitor* visitor) const = 0;
+  // The visitor (ExtensionsService) calls this function before it goes away.
+  virtual void ServiceShutdown() = 0;
+
+  // Enumerate registered extensions, calling
+  // OnExternalExtension(File|UpdateUrl)Found on the |visitor| object for each
+  // registered extension found.
+  virtual void VisitRegisteredExtension() const = 0;
 
   // Test if this provider has an extension with id |id| registered.
   virtual bool HasExtension(const std::string& id) const = 0;
@@ -53,6 +63,13 @@ class ExternalExtensionProvider {
   virtual bool GetExtensionDetails(const std::string& id,
                                    Extension::Location* location,
                                    scoped_ptr<Version>* version) const = 0;
+
+  // Determines if this provider had loaded the list of external extensions
+  // from its source.
+  virtual bool IsReady() = 0;
 };
 
+typedef std::vector<linked_ptr<ExternalExtensionProvider> >
+    ProviderCollection;
+
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTERNAL_EXTENSION_PROVIDER_H_