Implement the basic testing infrastructure for FindRequestManager.

content/browser/web_contents/web_contents_impl.h

Index: content/browser/web_contents/web_contents_impl.h
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index e136c089a42ebe0a20b12be03c0e3ffb08ff0c50..1bc7c3113ca3e13c2ee126cb073427a3a77e7eeb 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -774,6 +774,9 @@ private:
   FRIEND_TEST_ALL_PREFIXES(WebContentsImplBrowserTest,
                            JavaScriptDialogsInMainAndSubframes);
 
+  // So |find_request_manager_| can be accessed for testing.
+  friend class FindRequestManagerTest;
+
   // So InterstitialPageImpl can access SetIsLoading.
   friend class InterstitialPageImpl;