Adds unit tests for offline_pages::PrerenderAdapter calling PrerenderManager.

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 9ed133e1e47da0f834547c3440cdc62306aa096c..bba174aed0255f6507a238cc3bf8688b5d7e5890 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -55,6 +55,10 @@ namespace gfx {
 class Size;
 }
 
+namespace offline_pages {
+class UnitTestPrerenderManager;
+}
+
 namespace prerender {
 
 class PrerenderHandle;
@@ -394,6 +398,7 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
   friend class PrerenderContents;
   friend class PrerenderHandle;
   friend class UnitTestPrerenderManager;
+  friend class offline_pages::UnitTestPrerenderManager;
 
   class OnCloseWebContentsDeleter;
   struct NavigationRecord;