Add PanelOverflowStrip to handle panel overflow.

chrome/browser/ui/panels/base_panel_browser_test.cc

Index: chrome/browser/ui/panels/base_panel_browser_test.cc
diff --git a/chrome/browser/ui/panels/base_panel_browser_test.cc b/chrome/browser/ui/panels/base_panel_browser_test.cc
index 626d6b731ca4a2c5eee6f0120188ba3659907e24..89ed381fbe86c4db6c37e05c3a5d1098a65e30da 100644
--- a/chrome/browser/ui/panels/base_panel_browser_test.cc
+++ b/chrome/browser/ui/panels/base_panel_browser_test.cc
@@ -311,10 +311,15 @@ Panel* BasePanelBrowserTest::CreatePanelWithParams(
 #endif
   }
   MessageLoopForUI::current()->RunAllPending();
+
   // More waiting, because gaining or losing focus may require inter-process
   // asynchronous communication, and it is not enough to just run the local
   // message loop to make sure this activity has completed.
-  WaitForPanelActiveState(panel, params.show_flag);
+  // Note that overflow panel will not be shown as active.
+  ActiveState show_flag = params.show_flag;
+  if (panel->expansion_state() == Panel::IN_OVERFLOW)
+    show_flag = SHOW_AS_INACTIVE;
+  WaitForPanelActiveState(panel, show_flag);
 
   // On Linux, window size is not available right away and we should wait
   // before moving forward with the test.