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/libANGLE/State.cpp b/src/libANGLE/State.cpp
index ac7daab..c3c6701 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -244,7 +244,7 @@
     {
         mProgram->release(context);
     }
-    mProgram = NULL;
+    mProgram = nullptr;
 
     mTransformFeedback.set(NULL);
 
@@ -277,7 +277,7 @@
         buf.set(nullptr);
     }
 
-    mProgram = NULL;
+    mProgram = nullptr;
 
     angle::Matrix<GLfloat>::setToIdentity(mPathMatrixProj);
     angle::Matrix<GLfloat>::setToIdentity(mPathMatrixMV);
@@ -1039,7 +1039,7 @@
 {
     if (mVertexArray->id() == vertexArray)
     {
-        mVertexArray = NULL;
+        mVertexArray = nullptr;
         mDirtyBits.set(DIRTY_BIT_VERTEX_ARRAY_BINDING);
         mDirtyObjects.set(DIRTY_OBJECT_VERTEX_ARRAY);
         return true;