Support detaching/attaching panels via inter-strip drags.

chrome/browser/ui/panels/native_panel.h

Index: chrome/browser/ui/panels/native_panel.h
diff --git a/chrome/browser/ui/panels/native_panel.h b/chrome/browser/ui/panels/native_panel.h
index a2eb4e0563d8ba19a44b5f7850cda001bf4d252e..87ee8fe05528a294397cb285ef4af4df4f293a6e 100644
--- a/chrome/browser/ui/panels/native_panel.h
+++ b/chrome/browser/ui/panels/native_panel.h
@@ -87,6 +87,9 @@ class NativePanel {
   // Sets whether the panel app icon is visible (usually refers to the app icons
   // in the desktop bar).
   virtual void SetPanelAppIconVisibility(bool visible) = 0;
+
+  // Sets whether the panel window is always on top.
+  virtual void SetPanelAlwaysOnTop(bool on_top) = 0;
 };
 
 // A NativePanel utility interface used for accessing elements of the