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/EmulatePrecision.h b/src/compiler/translator/EmulatePrecision.h
index ec6bba5..08177b3 100644
--- a/src/compiler/translator/EmulatePrecision.h
+++ b/src/compiler/translator/EmulatePrecision.h
@@ -23,10 +23,10 @@
   public:
     EmulatePrecision(const TSymbolTable &symbolTable, int shaderVersion);
 
-    virtual void visitSymbol(TIntermSymbol *node);
-    virtual bool visitBinary(Visit visit, TIntermBinary *node);
-    virtual bool visitUnary(Visit visit, TIntermUnary *node);
-    virtual bool visitAggregate(Visit visit, TIntermAggregate *node);
+    void visitSymbol(TIntermSymbol *node) override;
+    bool visitBinary(Visit visit, TIntermBinary *node) override;
+    bool visitUnary(Visit visit, TIntermUnary *node) override;
+    bool visitAggregate(Visit visit, TIntermAggregate *node) override;
 
     void writeEmulationHelpers(TInfoSinkBase& sink, ShShaderOutput outputLanguage);