Give StatusTrayStateChangerProxy a virtual destructor.

This type has subclasses and is destroyed polymorphically, so the destructor
needs to be in the vtable. Found by clang.

Follow-up to https://codereview.chromium.org/252513004/

BUG=347693,82385
R=sky@chromium.org

Review URL: https://codereview.chromium.org/407653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284352 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/views/status_icons/status_tray_win.h

@@ -18,6 +18,8 @@ class StatusIconWin;
 // a task to a worker thread each time EnqueueChange is called.
 class StatusTrayStateChangerProxy {
  public:
+  virtual ~StatusTrayStateChangerProxy() {}
+
   // Called by StatusTrayWin to request upgraded visibility on the icon
   // represented by the |icon_id|, |window| pair.
   virtual void EnqueueChange(UINT icon_id, HWND window) = 0;