Refactoring: replace NULL by nullptr for pointers (2nd CL).

This CL mainly handles the pointer comparisons (== or !=).

BUG=angleproject:2001

Change-Id: I25ac3b61032e7ad91459a1c6541cadc87cf9b160
Reviewed-on: https://chromium-review.googlesource.com/483935
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/translator/VariableInfo.cpp b/src/compiler/translator/VariableInfo.cpp
index 9a806fc..bc84aea 100644
--- a/src/compiler/translator/VariableInfo.cpp
+++ b/src/compiler/translator/VariableInfo.cpp
@@ -106,7 +106,7 @@
 // shader.
 void CollectVariables::visitSymbol(TIntermSymbol *symbol)
 {
-    ASSERT(symbol != NULL);
+    ASSERT(symbol != nullptr);
     ShaderVariable *var       = nullptr;
     const TString &symbolName = symbol->getSymbol();