Add virtual and OVERRIDE to base/ implementation files

base/environment.cc

Index: base/environment.cc
diff --git a/base/environment.cc b/base/environment.cc
index 0bfc68e657b4888f0ddc7b059494973971b92822..34a236fd63a705a1951105f7901e24d51edc9e65 100644
--- a/base/environment.cc
+++ b/base/environment.cc
@@ -21,7 +21,8 @@ namespace {
 
 class EnvironmentImpl : public base::Environment {
  public:
-  virtual bool GetVar(const char* variable_name, std::string* result) {
+  virtual bool GetVar(const char* variable_name,
+                      std::string* result) OVERRIDE {
     if (GetVarImpl(variable_name, result))
       return true;
 
@@ -40,11 +41,12 @@ class EnvironmentImpl : public base::Environment {
     return GetVarImpl(alternate_case_var.c_str(), result);
   }
 
-  virtual bool SetVar(const char* variable_name, const std::string& new_value) {
+  virtual bool SetVar(const char* variable_name,
+                      const std::string& new_value) OVERRIDE {
     return SetVarImpl(variable_name, new_value);
   }
 
-  virtual bool UnSetVar(const char* variable_name) {
+  virtual bool UnSetVar(const char* variable_name) OVERRIDE {
     return UnSetVarImpl(variable_name);
   }