[Tab Scrolling] Workaround to hide horizontal scroll bars.

Horizontal Scroll bar visibility is currently coupled with its
functionality.

Bug: 1122214
Change-Id: I9a0c3ffb0e7128c4444b175631b7cbaf2411f7af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2393257
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804506}

chrome/browser/ui/views/frame/tab_strip_region_view.cc

@@ -28,7 +28,12 @@ TabStripRegionView::TabStripRegionView(std::unique_ptr<TabStrip> tab_strip) {
     views::ScrollView* tab_strip_scroll_container =
         AddChildView(std::make_unique<views::ScrollView>());
     tab_strip_scroll_container->SetBackgroundColor(base::nullopt);
-    tab_strip_scroll_container->SetHideHorizontalScrollBar(true);
+
+    // Temporary fix due to ScrollBar visibility coupling with scrolling.
+    // See https://crbug.com/1122214.
+    tab_strip_scroll_container->horizontal_scroll_bar()->SetPreferredSize(
+        gfx::Size());
+
     tab_strip_container_ = tab_strip_scroll_container;
     tab_strip_scroll_container->SetContents(std::move(tab_strip));
   } else {