Migrate HostZoomMap to live in StoragePartition.

content/public/browser/host_zoom_map.h

Index: content/public/browser/host_zoom_map.h
diff --git a/content/public/browser/host_zoom_map.h b/content/public/browser/host_zoom_map.h
index e65b443d2b4a64590e3aca78ef3ba45c3a0873d5..f5a06b2e54b24d255690b388a3f41db03817fcb7 100644
--- a/content/public/browser/host_zoom_map.h
+++ b/content/public/browser/host_zoom_map.h
@@ -13,11 +13,13 @@
 #include "base/callback.h"
 #include "base/callback_list.h"
 #include "content/common/content_export.h"
+#include "url/gurl.h"
 
 namespace content {
 
 class BrowserContext;
 class ResourceContext;
+class SiteInstance;
 class WebContents;
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
@@ -55,6 +57,11 @@ class HostZoomMap {
   CONTENT_EXPORT static HostZoomMap* GetForBrowserContext(
       BrowserContext* browser_context);
 
+  CONTENT_EXPORT static HostZoomMap* GetForSite(SiteInstance* instance);

[awong, 2014/08/11 22:36:33]

What does this mean semantically? 

Not saying this is bad necessarily, but a SiteInstance is a way to approximate
the grouping of "sites" that need to have scripting relations to one another.
Having a HostZoomMap attached to that without an explanation of why the
SiteInstance is the key seems a little odd...

[wjmaclean, 2014/08/12 16:57:44]

I'm assuming there's a one-to-one relationship between SiteInstances and
StoragePartition, hence a SiteInstance should identify a unique HostZoomMap.
Then the GetForWebContents() accessor is just a convenience.

The accessor via BrowserContext is for the default storage partition, which (at
least at present) is where we expect non-app/WebView pages to end up. UI
elements like wrench menu depend on this. *If* there are tabs displayed in the
main browser window that do not use the default storage partition, then some
issues may arise.

Is my assumption not correct?

Or is this more of a comment-documentation concern?

[Fady Samuel, 2014/08/13 19:45:42]

The signin page currently uses a different storage partition. This just occurred
to me.

+
+  CONTENT_EXPORT static HostZoomMap* GetForWebContents(
+      const WebContents* contents);
+
   // Returns the current zoom level for the specified WebContents. May be
   // temporary or host-specific.
   CONTENT_EXPORT static double GetZoomLevel(const WebContents* web_contents);