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/parseConst.cpp b/src/compiler/translator/parseConst.cpp
index 9c23551..0a6f7af 100644
--- a/src/compiler/translator/parseConst.cpp
+++ b/src/compiler/translator/parseConst.cpp
@@ -33,14 +33,14 @@
     bool error;
 
   protected:
-    void visitSymbol(TIntermSymbol *);
-    void visitConstantUnion(TIntermConstantUnion *);
-    bool visitBinary(Visit visit, TIntermBinary *);
-    bool visitUnary(Visit visit, TIntermUnary *);
-    bool visitSelection(Visit visit, TIntermSelection *);
-    bool visitAggregate(Visit visit, TIntermAggregate *);
-    bool visitLoop(Visit visit, TIntermLoop *);
-    bool visitBranch(Visit visit, TIntermBranch *);
+    void visitSymbol(TIntermSymbol *) override;
+    void visitConstantUnion(TIntermConstantUnion *) override;
+    bool visitBinary(Visit visit, TIntermBinary *) override;
+    bool visitUnary(Visit visit, TIntermUnary *) override;
+    bool visitSelection(Visit visit, TIntermSelection *) override;
+    bool visitAggregate(Visit visit, TIntermAggregate *) override;
+    bool visitLoop(Visit visit, TIntermLoop *) override;
+    bool visitBranch(Visit visit, TIntermBranch *) override;
 
     size_t mIndex;
     TConstantUnion *mUnionArray;