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 e9e523e29f477696cc635f0b1376cccd87967648..20bdaa15d2f836f3ef82c620d74a235ea9ac5762 100644
--- a/content/public/browser/host_zoom_map.h
+++ b/content/public/browser/host_zoom_map.h
@@ -20,6 +20,7 @@ namespace content {
 class NavigationEntry;
 class BrowserContext;
 class ResourceContext;
+class SiteInstance;
 class WebContents;
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
@@ -61,6 +62,17 @@ class HostZoomMap {
   CONTENT_EXPORT static HostZoomMap* GetDefaultForBrowserContext(
       BrowserContext* browser_context);
 
+  // Returns the HostZoomMap associated with this SiteInstance. The SiteInstance
+  // may serve multiple WebContents, and the HostZoomMap is the same for all of
+  // these WebContents.
+  CONTENT_EXPORT static HostZoomMap* Get(SiteInstance* instance);
+
+  // Returns the HostZoomMap associated with this WebContents. If multiple

[Charlie Reis, 2014/11/04 23:43:17]

These descriptions don't work out for out-of-process iframes.  A WebContents can
have frames from multiple different SiteInstances.

Do we expect the top-level frame's SiteInstance to dictate the zoom level for
the entire page, including all frames?  (That's how things work today, right?) 
In that case, we should clarify these comments to refer to the SiteInstance of
the WebContents's main frame.

(No need to make that work for OOPIF in this CL.)

[wjmaclean, 2014/11/05 21:55:42]

Done.

+  // WebContents share the same SiteInstance, then they share a single
+  // HostZoomMap.
+  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);