Material Refresh - When dragging tabs, don't track |hovered_tab|.

Bug: 853240
Change-Id: I8112807df34779c78e2d96ce15e391eb1863d8d1
Reviewed-on: https://chromium-review.googlesource.com/1112198Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Allen Bauer <kylixrd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569674}

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

@@ -1176,8 +1176,10 @@ void TabStrip::PaintChildren(const views::PaintInfo& paint_info) {
       } else if (!tab->IsActive()) {
         if (!tab->IsSelected()) {
           if (!stacked_layout_) {
-            // In Refresh mode, defer the painting of the hovered tab to below.
-            if (MD::IsRefreshUi() && tab->IsMouseHovered()) {
+            // In Refresh mode, defer the painting of the hovered tab to below
+            // unless a tab drag operation is in progress.
+            if (MD::IsRefreshUi() && tab->IsMouseHovered() &&
+                !(drag_controller_ && drag_controller_->started_drag())) {
               // Since two adjacent tabs overlap, they can both return as being
               // hovered. Favor the left-most tab by ensuring the current
               // |hovered_tab| is painted before assigning from |tab|.