Disable tabstrip-toolbar overlap with scrolling on.

Bug: 1093974
Change-Id: I1dcc65adb2f35c8269e8a6508d1165caf0f445cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630845Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843817}

chrome/browser/ui/layout_constants.cc

@@ -6,6 +6,7 @@
 
 #include "base/notreached.h"
 #include "components/omnibox/browser/omnibox_field_trial.h"
+#include "chrome/browser/ui/ui_features.h"
 #include "ui/base/pointer/touch_ui_controller.h"
 
 #if defined(OS_MAC)
@@ -76,6 +77,10 @@ int GetLayoutConstant(LayoutConstant constant) {
     case TABSTRIP_REGION_VIEW_CONTROL_PADDING:
       return 8;
     case TABSTRIP_TOOLBAR_OVERLAP:
+      // Because tab scrolling puts the tabstrip on a separate layer,
+      // changing paint order, this overlap isn't compatible with scrolling.
+      if (base::FeatureList::IsEnabled(features::kScrollableTabStrip))
+        return 0;
       return 1;
     case TOOLBAR_BUTTON_HEIGHT:
       return touch_ui ? 48 : 28;