Hide BrowsingInstance from all but SiteInstance, as intended by design.

content/browser/site_instance.h

Index: content/browser/site_instance.h
diff --git a/content/browser/site_instance.h b/content/browser/site_instance.h
index b85aa9ad4050882b08171fa53bac56497430bedc..215be44862a767db82571a383dc1a5b25c00919f 100644
--- a/content/browser/site_instance.h
+++ b/content/browser/site_instance.h
@@ -59,9 +59,6 @@ class CONTENT_EXPORT SiteInstance : public base::RefCounted<SiteInstance>,
   // Returns a unique ID for this SiteInstance.
   int32 id() { return id_; }
 
-  // Get the BrowsingInstance to which this SiteInstance belongs.
-  BrowsingInstance* browsing_instance() { return browsing_instance_; }
-
   // Sets the factory used to create new RenderProcessHosts. This will also be
   // passed on to SiteInstances spawned by this one.
   //
@@ -110,6 +107,10 @@ class CONTENT_EXPORT SiteInstance : public base::RefCounted<SiteInstance>,
   // navigating to the URL.
   bool HasWrongProcessForURL(const GURL& url) const;
 
+  // Browser context to which this SiteInstance (and all related
+  // SiteInstances) belongs.
+  content::BrowserContext* GetBrowserContext() const;
+
   // Factory method to create a new SiteInstance.  This will create a new
   // new BrowsingInstance, so it should only be used when creating a new tab
   // from scratch (or similar circumstances).  Callers should ensure that
@@ -195,6 +196,8 @@ class CONTENT_EXPORT SiteInstance : public base::RefCounted<SiteInstance>,
   // Whether SetSite has been called.
   bool has_site_;
 
+  FRIEND_TEST_ALL_PREFIXES(RenderViewHostManagerTest, NewTabPageProcesses);
+
   DISALLOW_COPY_AND_ASSIGN(SiteInstance);
 };