Vulkan/D3D11: Improve blit framebuffer tests and fix bug in D3D11

- Improving the tests revealed a bug in D3D 11 Fast Path rendering.
- These changes here are preliminary to implementing the blit for
depth/stencil in Vulkan when using the viewport flipping.

Bug: angleproject:2673
Bug: angleproject:2719
Change-Id: I6d55084e559d3110c8eeb0e7acb4e6fb09b6c1b5
Reviewed-on: https://chromium-review.googlesource.com/1132125
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Luc Ferron <lucferron@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
index 85ef146..89f22c3 100644
--- a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
+++ b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
@@ -485,6 +485,7 @@
         {
             if (flipSource || contextVk->isViewportFlipEnabledForReadFBO())
             {
+                // TODO(lucferron): Implement this http://anglebug.com/2673
                 // The tests in BlitFramebufferANGLETest are passing, but they are wrong since they
                 // use a single color for the depth / stencil buffers, it looks like its working,
                 // but if it was a gradient or a checked board, you would realize the flip isn't