Code refactoring: replace NULL by nullptr for pointers.

This is the frist change to replace NULL by nullptr.
It handles the initialization and assignment for pointers.

BUG=angleproject:2001

Change-Id: I6d4bb198a72e38b867cd2f65a6e6f2f61339a0b5
Reviewed-on: https://chromium-review.googlesource.com/481600
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/compiler/translator/VariableInfo.cpp b/src/compiler/translator/VariableInfo.cpp
index a201b4c..9a806fc 100644
--- a/src/compiler/translator/VariableInfo.cpp
+++ b/src/compiler/translator/VariableInfo.cpp
@@ -107,7 +107,7 @@
 void CollectVariables::visitSymbol(TIntermSymbol *symbol)
 {
     ASSERT(symbol != NULL);
-    ShaderVariable *var       = NULL;
+    ShaderVariable *var       = nullptr;
     const TString &symbolName = symbol->getSymbol();
 
     if (IsVarying(symbol->getQualifier()))