Vulkan: read pixel buffer alignment must be 4.

BUG=angleproject:2867

Change-Id: Ie14848bb464eea7f84d0ce523dff2cddf7a185d4
Reviewed-on: https://chromium-review.googlesource.com/c/1260256
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
index cfa5624..a43eae9 100644
--- a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
+++ b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
@@ -127,7 +127,7 @@
       mBlitPixelBuffer(VK_BUFFER_USAGE_TRANSFER_SRC_BIT, kMinReadPixelsBufferSize)
 {
     mBlitPixelBuffer.init(1, renderer);
-    mReadPixelBuffer.init(1, renderer);
+    mReadPixelBuffer.init(4, renderer);
 }
 
 FramebufferVk::~FramebufferVk() = default;