Vulkan: work around vkCmdCopyBuffer bug.

It seems that vkCmdCopyBuffer on Windows with Intel GPU neglects
the last region when given more than one.  Work around that in
LineLoopHelper::getIndexBufferForElementArrayBuffer() by adding an
unused region.  Enable corresponding test.

BUG=angleproject:2838

Change-Id: I8847c7b2cfdb94526d4d28ba5bf1f162da3a1ed4
Reviewed-on: https://chromium-review.googlesource.com/1238887
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/RendererVk.cpp b/src/libANGLE/renderer/vulkan/RendererVk.cpp
index 9ac899b..cf543f5 100644
--- a/src/libANGLE/renderer/vulkan/RendererVk.cpp
+++ b/src/libANGLE/renderer/vulkan/RendererVk.cpp
@@ -689,6 +689,11 @@
     // TODO(lucferron): Currently disabled on Intel only since many tests are failing and need
     // investigation. http://anglebug.com/2728
     mFeatures.flipViewportY = !IsIntel(mPhysicalDeviceProperties.vendorID);
+
+#ifdef ANGLE_PLATFORM_WINDOWS
+    // http://anglebug.com/2838
+    mFeatures.extraCopyBufferRegion = IsIntel(mPhysicalDeviceProperties.vendorID);
+#endif
 }
 
 void RendererVk::ensureCapsInitialized() const