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/renderer/d3d/FramebufferD3D.cpp b/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
index 8b37657..620b374 100644
--- a/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
+++ b/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
@@ -197,7 +197,7 @@
         return GL_NONE;
     }
 
-    RenderTargetD3D *attachmentRenderTarget = NULL;
+    RenderTargetD3D *attachmentRenderTarget = nullptr;
     gl::Error error = readAttachment->getRenderTarget(&attachmentRenderTarget);
     if (error.isError())
     {
@@ -220,7 +220,7 @@
         return GL_NONE;
     }
 
-    RenderTargetD3D *attachmentRenderTarget = NULL;
+    RenderTargetD3D *attachmentRenderTarget = nullptr;
     gl::Error error = readAttachment->getRenderTarget(&attachmentRenderTarget);
     if (error.isError())
     {