[chromedriver] Support clicking an element in sub frames.

chrome/test/chromedriver/session_commands.cc

Index: chrome/test/chromedriver/session_commands.cc
diff --git a/chrome/test/chromedriver/session_commands.cc b/chrome/test/chromedriver/session_commands.cc
index a24f1e2f8b3ca4412bfe02833eb599169a4726b9..5502d9301b9e7fdd510e2120b97fda8cbfbe7ec4 100644
--- a/chrome/test/chromedriver/session_commands.cc
+++ b/chrome/test/chromedriver/session_commands.cc
@@ -167,7 +167,7 @@ Status ExecuteSwitchToWindow(
   if (!web_view)
     return Status(kNoSuchWindow);
   session->window = web_view->GetId();
-  session->frame = "";
+  session->SwitchToTopFrame();
   session->mouse_position = WebPoint(0, 0);
   return Status(kOk);
 }
@@ -281,7 +281,8 @@ Status ExecuteIsLoading(
     return status;
 
   bool is_pending;
-  status = web_view->IsPendingNavigation(session->frame, &is_pending);
+  status = web_view->IsPendingNavigation(
+      session->GetCurrentFrameId(), &is_pending);
   if (status.IsError())
     return status;
   value->reset(new base::FundamentalValue(is_pending));