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 53b3e2f2e6e64238d7dcc757ea2c6cb3aa86d13e..0898919a6e90b83de7398f019d2b42bb84620f41 100644
--- a/chrome/browser/ui/panels/native_panel.h
+++ b/chrome/browser/ui/panels/native_panel.h
@@ -88,6 +88,9 @@ 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