[Tab Scrolling] Position NTB correctly.

Bug: 1094033
Change-Id: If3fb879e2624833eb8448a61bab57891258f17bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2241646Reviewed-by: Connie Wan <connily@chromium.org>
Commit-Queue: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777560}

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -3180,10 +3180,13 @@ void TabStrip::UpdateIdealBounds() {
     const int trailing_x =
         layout_helper_->UpdateIdealBounds(available_width_for_tabs);
 
+    int ntb_x_offset =
+        base::FeatureList::IsEnabled(features::kScrollableTabStrip)
+            ? trailing_x
+            : std::min(available_width_for_tabs, trailing_x);
+
     new_tab_button_ideal_bounds_.set_origin(
-        gfx::Point(std::min(available_width_for_tabs, trailing_x) +
-                       TabToNewTabButtonSpacing(),
-                   0));
+        gfx::Point(ntb_x_offset + TabToNewTabButtonSpacing(), 0));
   }
 }