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

chrome/common/extensions/features/base_feature_provider.cc

Index: chrome/common/extensions/features/base_feature_provider.cc
diff --git a/chrome/common/extensions/features/base_feature_provider.cc b/chrome/common/extensions/features/base_feature_provider.cc
index 506e1b6e7a569758b9c7ec4b71371584d041a70f..285426d147d108f684711b6ef13a51a177ddc7e8 100644
--- a/chrome/common/extensions/features/base_feature_provider.cc
+++ b/chrome/common/extensions/features/base_feature_provider.cc
@@ -32,11 +32,11 @@ class LazyFeatureProvider : public FeatureProvider {
         resource_id_(resource_id) {
   }
 
-  virtual Feature* GetFeature(const std::string& name) {
+  virtual Feature* GetFeature(const std::string& name) OVERRIDE {
     return GetBaseFeatureProvider()->GetFeature(name);
   }
 
-  virtual std::set<std::string> GetAllFeatureNames() {
+  virtual std::set<std::string> GetAllFeatureNames() OVERRIDE {
     return GetBaseFeatureProvider()->GetAllFeatureNames();
   }