First cut at Exit Fullscreen bubble on Linux.

chrome/browser/gtk/browser_window_gtk.h

Index: chrome/browser/gtk/browser_window_gtk.h
diff --git a/chrome/browser/gtk/browser_window_gtk.h b/chrome/browser/gtk/browser_window_gtk.h
index 6d79a9ac77e7d493f5b4be70199824541b78aa81..f531a65abfb28fb8edf8d14d863e7fac2d33fd2e 100644
--- a/chrome/browser/gtk/browser_window_gtk.h
+++ b/chrome/browser/gtk/browser_window_gtk.h
@@ -35,6 +35,7 @@ class BrowserToolbarGtk;
 class CustomDrawButton;
 class DownloadShelfGtk;
 class FindBarGtk;
+class FullscreenExitBubbleGtk;
 class InfoBarContainerGtk;
 class LocationBar;
 class StatusBubbleGtk;
@@ -430,6 +431,8 @@ class BrowserWindowGtk : public BrowserWindow,
   // The accelerator group used to handle accelerators, owned by this object.
   GtkAccelGroup* accel_group_;
 
+  scoped_ptr<FullscreenExitBubbleGtk> fullscreen_exit_bubble_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserWindowGtk);
 };