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/libANGLE/State.cpp b/src/libANGLE/State.cpp
index c3c6701..b29969b 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -1025,13 +1025,13 @@
 
 GLuint State::getVertexArrayId() const
 {
-    ASSERT(mVertexArray != NULL);
+    ASSERT(mVertexArray != nullptr);
     return mVertexArray->id();
 }
 
 VertexArray *State::getVertexArray() const
 {
-    ASSERT(mVertexArray != NULL);
+    ASSERT(mVertexArray != nullptr);
     return mVertexArray;
 }