Use override in all the places where it is possible

This will avoid -Winconsistent-overrides in the future. Done using the
-Wsuggest-override warning of GCC 5.1

BUG=

Change-Id: I707a649dc368f5dd1e139fd144370abcac0b6263
Reviewed-on: https://chromium-review.googlesource.com/294920
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/compiler/translator/ValidateLimitations.h b/src/compiler/translator/ValidateLimitations.h
index 59cccb5..ec8891b 100644
--- a/src/compiler/translator/ValidateLimitations.h
+++ b/src/compiler/translator/ValidateLimitations.h
@@ -21,10 +21,10 @@
 
     int numErrors() const { return mNumErrors; }
 
-    virtual bool visitBinary(Visit, TIntermBinary *);
-    virtual bool visitUnary(Visit, TIntermUnary *);
-    virtual bool visitAggregate(Visit, TIntermAggregate *);
-    virtual bool visitLoop(Visit, TIntermLoop *);
+    bool visitBinary(Visit, TIntermBinary *) override;
+    bool visitUnary(Visit, TIntermUnary *) override;
+    bool visitAggregate(Visit, TIntermAggregate *) override;
+    bool visitLoop(Visit, TIntermLoop *) override;
 
   private:
     void error(TSourceLoc loc, const char *reason, const char *token);