Update prerender policy for custom tabs

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index fdf874e3d3f8f5b0652c30b48241c0ba4c2f23fa..c33c540657d6824793f8f84767a7b6c91f52eb00 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -134,6 +134,14 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
       content::SessionStorageNamespace* session_storage_namespace,
       const gfx::Size& size);
 
+  // Adds a prerender from an external request that will prerender even on
+  // cellular networks as long as the user setting for prerendering is ON.
+  PrerenderHandle* AddPrerenderOnCellularFromExternalRequest(
+      const GURL& url,
+      const content::Referrer& referrer,
+      content::SessionStorageNamespace* session_storage_namespace,
+      const gfx::Size& size);
+
   // Adds a prerender for Instant Search |url| if valid. The
   // |session_storage_namespace| matches the namespace of the active tab at the
   // time the prerender is generated. Returns a caller-owned PrerenderHandle* or
@@ -395,6 +403,11 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
   // disabled.
   chrome_browser_net::NetworkPredictionStatus GetPredictionStatus() const;
 
+  // Returns whether prerendering is currently enabled or the reason why it is
+  // disabled after taking into account the origin of the request.
+  chrome_browser_net::NetworkPredictionStatus GetPredictionStatusForOrigin(
+      Origin origin) const;
+
   // Adds a prerender for |url| from |referrer|. The |origin| specifies how the
   // prerender was added. If |size| is empty, then
   // PrerenderContents::StartPrerendering will instead use a default from