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/ProgramD3D.cpp b/src/libANGLE/renderer/d3d/ProgramD3D.cpp
index 4563d7d..4af20fc 100644
--- a/src/libANGLE/renderer/d3d/ProgramD3D.cpp
+++ b/src/libANGLE/renderer/d3d/ProgramD3D.cpp
@@ -1176,7 +1176,7 @@
         mPixelHLSL, mPixelShaderKey, mUsesFragDepth, outputSignature);
 
     // Generate new pixel executable
-    ShaderExecutableD3D *pixelExecutable = NULL;
+    ShaderExecutableD3D *pixelExecutable = nullptr;
 
     gl::InfoLog tempInfoLog;
     gl::InfoLog *currentInfoLog = infoLog ? infoLog : &tempInfoLog;
@@ -1221,7 +1221,7 @@
         mVertexHLSL, inputLayout, mState.getAttributes());
 
     // Generate new vertex executable
-    ShaderExecutableD3D *vertexExecutable = NULL;
+    ShaderExecutableD3D *vertexExecutable = nullptr;
 
     gl::InfoLog tempInfoLog;
     gl::InfoLog *currentInfoLog = infoLog ? infoLog : &tempInfoLog;