Vulkan: Shader path for framebuffer-to-texture copy

Part 1 in a series of changes to perform image copies on the GPU.

Bug: angleproject:2958
Change-Id: I6264a880865c4738c0866f2dc71af63425fc4118
Reviewed-on: https://chromium-review.googlesource.com/c/1370724
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/RenderbufferVk.cpp b/src/libANGLE/renderer/vulkan/RenderbufferVk.cpp
index 2d43f8a..c6e8907 100644
--- a/src/libANGLE/renderer/vulkan/RenderbufferVk.cpp
+++ b/src/libANGLE/renderer/vulkan/RenderbufferVk.cpp
@@ -77,6 +77,8 @@
 
         VkImageAspectFlags aspect = vk::GetFormatAspectFlags(textureFormat);
 
+        // Note that LUMA textures are not color-renderable, so a read-view with swizzle is not
+        // needed.
         ANGLE_TRY(mImage.initImageView(contextVk, gl::TextureType::_2D, aspect, gl::SwizzleState(),
                                        &mImageView, 1));