Add test cases for panel overflow handling.

chrome/browser/ui/panels/panel_strip.cc

Index: chrome/browser/ui/panels/panel_strip.cc
diff --git a/chrome/browser/ui/panels/panel_strip.cc b/chrome/browser/ui/panels/panel_strip.cc
index 27d5e1ba483dcede7125bad3261c6fcd77f34f60..a2aad2eca031a33d035ffeae319156cf3c7b3bba 100644
--- a/chrome/browser/ui/panels/panel_strip.cc
+++ b/chrome/browser/ui/panels/panel_strip.cc
@@ -180,7 +180,12 @@ bool PanelStrip::Remove(Panel* panel) {
   }
 
   DoRemove(panel);
-  Rearrange();
+
+  // Don't rearrange the strip if a panel is being moved from the panel strip
+  // to the overflow strip.
+  if (panel->expansion_state() != Panel::IN_OVERFLOW)
+    Rearrange();
+
   return true;
 }