Migrate HostZoomMap to live in StoragePartition.

chrome/browser/ui/zoom/zoom_controller.h

Index: chrome/browser/ui/zoom/zoom_controller.h
diff --git a/chrome/browser/ui/zoom/zoom_controller.h b/chrome/browser/ui/zoom/zoom_controller.h
index db771ee3084c55d718fca57d49765f572a7d05a8..7dad4ad35ec9f9b6e3336d02920f231fdbc01442 100644
--- a/chrome/browser/ui/zoom/zoom_controller.h
+++ b/chrome/browser/ui/zoom/zoom_controller.h
@@ -73,10 +73,8 @@ class ZoomController : public content::WebContentsObserver,
   // Convenience method to get default zoom level. Implemented here for
   // inlining.
   double GetDefaultZoomLevel() const {
-    // TODO(wjmaclean) Make this refer to the webcontents-specific HostZoomMap
-    // when that becomes available.
-    return content::HostZoomMap::GetDefaultForBrowserContext(browser_context_)->
-        GetDefaultZoomLevel();
+    return content::HostZoomMap::GetForWebContents(web_contents())
+        ->GetDefaultZoomLevel();
   }
 
   // Convenience method to quickly check if the tab's at default zoom.