Refactoring: replace NULL by nullptr for pointers (3rd CL).

This CL mainly handles passing/returning NULL to/from a function.

BUG=angleproject:2001

Change-Id: I34802f792e710e3d7ff697cbe4701dc1bf5ab009
Reviewed-on: https://chromium-review.googlesource.com/485060
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/tests/gl_tests/TextureTest.cpp b/src/tests/gl_tests/TextureTest.cpp
index 6d5b12f..e8279e5 100644
--- a/src/tests/gl_tests/TextureTest.cpp
+++ b/src/tests/gl_tests/TextureTest.cpp
@@ -121,7 +121,7 @@
         GLuint texture2D;
         glGenTextures(1, &texture2D);
         glBindTexture(GL_TEXTURE_2D, texture2D);
-        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
         EXPECT_GL_NO_ERROR();
         return texture2D;
     }
@@ -1473,7 +1473,7 @@
 
         // Initializes the color of the upper-left 8x8 pixels, leaves the other pixels untouched.
         // glTexSubImage2D should take into account that the image is dirty.
-        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 8, 8, GL_RGB, GL_UNSIGNED_BYTE, NULL);
+        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 8, 8, GL_RGB, GL_UNSIGNED_BYTE, nullptr);
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);