Vulkan: Add CommandGraph class.

This also renames CommandBufferNode to CommandGraphNode. It also
renames some of the intenal members to more closely represent the
tree relationships (parents/children). This should clean up the
command graph classes and make them a bit easier to understand.

Bug: angleproject:2361
Change-Id: I024bffcc7f4157c78072ef902a3c40a07a08b18a
Reviewed-on: https://chromium-review.googlesource.com/922121
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp b/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
index de04ea5..89d83a9 100644
--- a/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
+++ b/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
@@ -13,7 +13,7 @@
 
 #include "libANGLE/Context.h"
 #include "libANGLE/renderer/vulkan/BufferVk.h"
-#include "libANGLE/renderer/vulkan/CommandBufferNode.h"
+#include "libANGLE/renderer/vulkan/CommandGraph.h"
 #include "libANGLE/renderer/vulkan/ContextVk.h"
 #include "libANGLE/renderer/vulkan/vk_format_utils.h"
 
@@ -163,7 +163,7 @@
     return mCurrentArrayBufferOffsets;
 }
 
-void VertexArrayVk::updateDrawDependencies(vk::CommandBufferNode *readNode,
+void VertexArrayVk::updateDrawDependencies(vk::CommandGraphNode *readNode,
                                            const gl::AttributesMask &activeAttribsMask,
                                            Serial serial,
                                            DrawType drawType)