Update {virtual,override} to follow C++11 style in chrome.

chrome/browser/ui/views/panels/panel_stack_view.h

Index: chrome/browser/ui/views/panels/panel_stack_view.h
diff --git a/chrome/browser/ui/views/panels/panel_stack_view.h b/chrome/browser/ui/views/panels/panel_stack_view.h
index 5abe1e72878a9a4ef168e8fb4de40a927d13ace5..56f8ce87aebca8d6be0dc753b330951ec8ee88a7 100644
--- a/chrome/browser/ui/views/panels/panel_stack_view.h
+++ b/chrome/browser/ui/views/panels/panel_stack_view.h
@@ -94,14 +94,14 @@ class PanelStackView : public NativePanelStackWindow,
 
 #if defined(OS_WIN)
   // Overridden from ui::HWNDMessageFilter:
-  virtual bool FilterMessage(HWND hwnd,
-                             UINT message,
-                             WPARAM w_param,
-                             LPARAM l_param,
-                             LRESULT* l_result) override;
+  bool FilterMessage(HWND hwnd,
+                     UINT message,
+                     WPARAM w_param,
+                     LPARAM l_param,
+                     LRESULT* l_result) override;
 
   // Overridden from TaskbarWindowThumbnailerDelegateWin:
-  virtual std::vector<HWND> GetSnapshotWindowHandles() const override;
+  std::vector<HWND> GetSnapshotWindowHandles() const override;
 
   // Updates the live preview snapshot when something changes, like
   // adding/removing/moving/resizing a stacked panel.