Convert NULL and 0 to nullptr.

This was created by looking at warnings produced by clang's
-Wzero-as-null-pointer-constant. This updates most issues in
Skia code. However, there are places where GL and Vulkan want
pointer values which are explicitly 0, external headers which
use NULL directly, and possibly more uses in un-compiled
sources (for other platforms).

Change-Id: Id22fbac04d5c53497a53d734f0896b4f06fe8345
Reviewed-on: https://skia-review.googlesource.com/39521
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index 83d28de..f32a83a 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -1070,7 +1070,7 @@
     VkImageAspectFlags aspectFlags = VK_IMAGE_ASPECT_COLOR_BIT;
     VkImageMemoryBarrier imageMemoryBarrier = {
         VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER,          // sType
-        NULL,                                            // pNext
+        nullptr,                                         // pNext
         VK_ACCESS_TRANSFER_WRITE_BIT,                    // srcAccessMask
         VK_ACCESS_TRANSFER_READ_BIT,                     // dstAccessMask
         VK_IMAGE_LAYOUT_GENERAL,                         // oldLayout
@@ -1213,7 +1213,7 @@
 
     const VkImageCreateInfo imageCreateInfo = {
         VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO,         // sType
-        NULL,                                        // pNext
+        nullptr,                                     // pNext
         0,                                           // VkImageCreateFlags
         VK_IMAGE_TYPE_2D,                            // VkImageType
         pixelFormat,                                 // VkFormat
@@ -1295,7 +1295,7 @@
 
         const VkCommandBufferAllocateInfo cmdInfo = {
             VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,   // sType
-            NULL,                                             // pNext
+            nullptr,                                          // pNext
             fCmdPool,                                         // commandPool
             VK_COMMAND_BUFFER_LEVEL_PRIMARY,                  // level
             1                                                 // bufferCount