Add unit test and supporting code to test process overflow case.

chrome/browser/renderer_host/site_instance.h

Index: chrome/browser/renderer_host/site_instance.h
diff --git a/chrome/browser/renderer_host/site_instance.h b/chrome/browser/renderer_host/site_instance.h
index 98807d0faf71e753759d99c9732d35353d01e683..3be920c50254abbfcf9046ded2181c02b630895d 100644
--- a/chrome/browser/renderer_host/site_instance.h
+++ b/chrome/browser/renderer_host/site_instance.h
@@ -132,6 +132,9 @@ class SiteInstance : public base::RefCounted<SiteInstance>,
   static bool IsSameWebSite(Profile* profile,
                             const GURL& url1, const GURL& url2);
 
+  // Returns the renderer type for this URL.
+  static RenderProcessHost::Type RendererTypeForURL(const GURL& url);
+
  protected:
   friend class base::RefCounted<SiteInstance>;
   friend class BrowsingInstance;