Extension Storage API: expose storage quota information to extensions, via:

chrome/browser/extensions/settings/settings_frontend.h

Index: chrome/browser/extensions/settings/settings_frontend.h
diff --git a/chrome/browser/extensions/settings/settings_frontend.h b/chrome/browser/extensions/settings/settings_frontend.h
index e007b9fc07e3fc5f13d4a9b338e40fe90d30e18c..5202d2966922bffe6120b53069a4a70f1d59d9b5 100644
--- a/chrome/browser/extensions/settings/settings_frontend.h
+++ b/chrome/browser/extensions/settings/settings_frontend.h
@@ -16,6 +16,7 @@
 #include "chrome/browser/extensions/settings/settings_leveldb_storage.h"
 #include "chrome/browser/extensions/settings/settings_namespace.h"
 #include "chrome/browser/extensions/settings/settings_observer.h"
+#include "chrome/browser/extensions/settings/settings_storage_quota_enforcer.h"
 #include "chrome/browser/sync/api/syncable_service.h"
 
 class Profile;
@@ -29,9 +30,15 @@ class SettingsStorage;
 // All public methods must be called on the UI thread.
 class SettingsFrontend {
  public:
-  // Creates with the default factory.  Ownership of |profile| not taken.
+  // Quota limits for sync and local. Make these public for tests.
+  static const SettingsStorageQuotaEnforcer::Limits kSyncQuota;
+  static const SettingsStorageQuotaEnforcer::Limits kLocalQuota;
+
+  // Creates with the default factory. Ownership of |profile| not taken.
   static SettingsFrontend* Create(Profile* profile);
 
+  // Creates with a specific factory |storage_factory| (presumably for tests).
+  // Ownership of |profile| not taken.
   static SettingsFrontend* Create(
       const scoped_refptr<SettingsStorageFactory>& storage_factory,
       // Owership NOT taken.