Clean up binary operation constant folding code

Fix mixed up comments, remove unnecessary type conversions, clarify
variable names and improve formatting in a few places.

TEST=angle_unittests, WebGL conformance tests
BUG=angleproject:913

Change-Id: Ice8fe3682d8e97f42747752302a1fba116132df4
Reviewed-on: https://chromium-review.googlesource.com/266843
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
diff --git a/src/compiler/translator/Intermediate.cpp b/src/compiler/translator/Intermediate.cpp
index ecc6915..ebe6c39 100644
--- a/src/compiler/translator/Intermediate.cpp
+++ b/src/compiler/translator/Intermediate.cpp
@@ -143,7 +143,7 @@
 
     if (childTempConstant)
     {
-        TIntermTyped *newChild = childTempConstant->fold(op, 0, mInfoSink);
+        TIntermTyped *newChild = childTempConstant->fold(op, nullptr, mInfoSink);
 
         if (newChild)
             return newChild;