Observe adding external extensions via windows registry.

extensions/browser/external_provider_interface.h

Index: extensions/browser/external_provider_interface.h
diff --git a/extensions/browser/external_provider_interface.h b/extensions/browser/external_provider_interface.h
index 801f4ede5640de99259898da3c2b0e22cbb9e336..09d9950966ddc39cfca6e33fa16dbf11ebfc9dea 100644
--- a/extensions/browser/external_provider_interface.h
+++ b/extensions/browser/external_provider_interface.h
@@ -8,12 +8,12 @@
 #include <vector>
 
 #include "base/memory/linked_ptr.h"
+#include "extensions/browser/external_extension_install_info.h"
 #include "extensions/common/manifest.h"
 
 class GURL;
 
 namespace base {
-class FilePath;
 class Version;
 }
 
@@ -35,24 +35,14 @@ class ExternalProviderInterface {
     // proceed if the extension is already installed from a higher priority
     // location.
     virtual bool OnExternalExtensionFileFound(
-        const std::string& id,
-        const base::Version* version,
-        const base::FilePath& path,
-        Manifest::Location location,
-        int creation_flags,
-        bool mark_acknowledged,
-        bool install_immediately) = 0;
+        ExternalExtensionInstallInfoFile* info) = 0;

[asargent_no_longer_on_chrome, 2016/01/25 18:50:52]

nit: If ownership of this data is passed, this should probably use
scoped_ptr<ExternalExtensionInstallInfoFile> to make that clear. If ownership
isn't passed, it should use const ExternalExtensionInstallInfoFile& (I assume it
wouldn't be useful to be able to pass nullptr)

[lazyboy, 2016/01/26 05:20:05]

Done.

 
     // Return true if the extension install will proceed.  Install might not
     // proceed if the extension is already installed from a higher priority
     // location.
     virtual bool OnExternalExtensionUpdateUrlFound(
-        const std::string& id,
-        const std::string& install_parameter,
-        const GURL& update_url,
-        Manifest::Location location,
-        int creation_flags,
-        bool mark_acknowledged) = 0;
+        ExternalExtensionInstallInfoUpdateUrl* info,

[asargent_no_longer_on_chrome, 2016/01/25 18:50:52]

same comment re: ownership

[lazyboy, 2016/01/26 05:20:05]

Done.

+        bool is_initial_load) = 0;
 
     // Called after all the external extensions have been reported
     // through the above two methods. |provider| is a pointer to the
@@ -62,6 +52,18 @@ class ExternalProviderInterface {
     virtual void OnExternalProviderReady(
         const ExternalProviderInterface* provider) = 0;
 
+    // Once this provider becomes "ready", it can send additional external
+    // extensions it learns about later on through
+    // OnExternalExtensionUpdateUrlFound() or OnExternalExtensionFileFound().
+    // This method will be called each time the provider finds a set of
+    // updated external extensions.
+    virtual void OnExternalProviderUpdateComplete(
+        const ExternalProviderInterface* provider,
+        const ScopedVector<ExternalExtensionInstallInfoUpdateUrl>&
+            update_url_extensions,
+        const ScopedVector<ExternalExtensionInstallInfoFile>& file_extensions,
+        const std::set<std::string>& removed_extensions) = 0;
+
    protected:
     virtual ~VisitorInterface() {}
   };