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/third_party/compiler/ArrayBoundsClamper.cpp b/src/third_party/compiler/ArrayBoundsClamper.cpp
index 7c68e82..fa6c8b8 100644
--- a/src/third_party/compiler/ArrayBoundsClamper.cpp
+++ b/src/third_party/compiler/ArrayBoundsClamper.cpp
@@ -48,7 +48,7 @@
    {
    }
 
-   virtual bool visitBinary(Visit visit, TIntermBinary* node)
+    bool visitBinary(Visit visit, TIntermBinary *node) override
    {
        if (node->getOp() == EOpIndexIndirect)
        {