WebXR: Fix viewport height calculation in GetViewportForLayer

Use GetVerticalViewCount() to correctly compute the viewport height in
GetViewportForLayer.

Bug: 468035615
Change-Id: I29840be73ff710c9e5326802b56d88719bd61efe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7254815
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Ho Cheung <hocheung@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1558337}

AUTHORS

diff --git a/AUTHORS b/AUTHORS
index d99946b..4d89f58 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1745,6 +1745,7 @@
 Zhenyu Shan <zhenyu.shan@intel.com>
 Zhibo Wang <zhibo1.wang@intel.com>
 Zhifei Fang <facetothefate@gmail.com>
+Zhixin Tu <tuzhixin25@gmail.com>
 Zhiyuan Ye <zhiyuanye@tencent.com>
 Zhongwei Wang <carolwolfking@gmail.com>
 Zhou Jun <zhoujun@uniontech.com>

third_party/blink/renderer/modules/xr/xr_webgl_binding.cc

diff --git a/third_party/blink/renderer/modules/xr/xr_webgl_binding.cc b/third_party/blink/renderer/modules/xr/xr_webgl_binding.cc
index aa05fe2..6e92f441 100644
--- a/third_party/blink/renderer/modules/xr/xr_webgl_binding.cc
+++ b/third_party/blink/renderer/modules/xr/xr_webgl_binding.cc
@@ -366,7 +366,7 @@
   uint32_t width =
       layer.textureWidth() / GetHorizontalViewCount(layer.layout());
   uint32_t height =
-      layer.textureHeight() / GetHorizontalViewCount(layer.layout());
+      layer.textureHeight() / GetVerticalViewCount(layer.layout());
 
   if (eye == V8XREye::Enum::kRight &&
       (layer.layout() == V8XRLayerLayout::Enum::kStereoTopBottom ||