Cleanup to keep panel from manipulating its panel strip assignment directly.

chrome/browser/ui/panels/panel_strip.h

Index: chrome/browser/ui/panels/panel_strip.h
diff --git a/chrome/browser/ui/panels/panel_strip.h b/chrome/browser/ui/panels/panel_strip.h
index 7b0bced6fc2a6b29013fbc85f8db791ffa6d87dd..f5db53839205ffe3dbc0bfa6a8bc74201bff799c 100644
--- a/chrome/browser/ui/panels/panel_strip.h
+++ b/chrome/browser/ui/panels/panel_strip.h
@@ -36,8 +36,7 @@ class PanelStrip {
 
   // Removes |panel| from the collection of panels. Invoked asynchronously
   // after a panel has been closed.
-  // Returns |false| if the panel is not in the strip.
-  virtual bool RemovePanel(Panel* panel) = 0;
+  virtual void RemovePanel(Panel* panel) = 0;
 
   // Closes all panels in the collection. Panels will be removed after closing.
   virtual void CloseAll() = 0;