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

chrome/browser/extensions/settings/settings_api.h

Index: chrome/browser/extensions/settings/settings_api.h
diff --git a/chrome/browser/extensions/settings/settings_api.h b/chrome/browser/extensions/settings/settings_api.h
index d8d2d5e99cf1a22529b5e1e4f2577081c275589a..1728e9f550f84236dacdb3494360342bbe2264b3 100644
--- a/chrome/browser/extensions/settings/settings_api.h
+++ b/chrome/browser/extensions/settings/settings_api.h
@@ -99,6 +99,14 @@ class ClearSettingsFunction : public SettingsFunction {
       QuotaLimitHeuristics* heuristics) const OVERRIDE;
 };
 
+class GetBytesInUseSettingsFunction : public SettingsFunction {
+ public:
+  DECLARE_EXTENSION_FUNCTION_NAME("storage.getBytesInUse");
+
+ protected:
+  virtual bool RunWithStorage(SettingsStorage* storage) OVERRIDE;
+};
+
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_SETTINGS_SETTINGS_API_H_