Warn on missing OVERRIDE/virtual everywhere, not just in header files.

ash/wm/partial_screenshot_view_unittest.cc

Index: ash/wm/partial_screenshot_view_unittest.cc
diff --git a/ash/wm/partial_screenshot_view_unittest.cc b/ash/wm/partial_screenshot_view_unittest.cc
index ea1d54c111fe28a7226c76f1c71bfabcdca985e1..a763577d0ef935e735ee5a0ebc39f6be582198cb 100644
--- a/ash/wm/partial_screenshot_view_unittest.cc
+++ b/ash/wm/partial_screenshot_view_unittest.cc
@@ -17,14 +17,14 @@ class FakeScreenshotDelegate : public ScreenshotDelegate {
  public:
   FakeScreenshotDelegate() : screenshot_count_(0) {}
 
-  void HandleTakeScreenshotForAllRootWindows() OVERRIDE {}
-  void HandleTakePartialScreenshot(aura::Window* window,
-                                   const gfx::Rect& rect) OVERRIDE {
+  virtual void HandleTakeScreenshotForAllRootWindows() OVERRIDE {}
+  virtual void HandleTakePartialScreenshot(aura::Window* window,
+                                           const gfx::Rect& rect) OVERRIDE {
     rect_ = rect;
     screenshot_count_++;
   }
 
-  bool CanTakeScreenshot() OVERRIDE {
+  virtual bool CanTakeScreenshot() OVERRIDE {
     return true;
   }