Add finch control for the new tab button position in Refresh.

We need to be able to change this later without a merge.

Bug: 848420
Change-Id: Ie4f50f6a919e5e4e761c364776c702d40513637d
Reviewed-on: https://chromium-review.googlesource.com/1111209Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569667}

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

@@ -8,6 +8,7 @@
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/metrics/user_metrics.h"
 #include "build/build_config.h"
@@ -61,6 +62,9 @@ using content::WebContents;
 
 namespace {
 
+const base::Feature kRefreshNewTabButtonAfterTabs = {
+    "RefreshNewTabButtonAfterTabs", base::FEATURE_DISABLED_BY_DEFAULT};
+
 bool DetermineTabStripLayoutStacked(PrefService* prefs, bool* adjust_layout) {
   *adjust_layout = false;
   // For ash, always allow entering stacked mode.
@@ -309,8 +313,10 @@ bool BrowserTabStripController::IsCompatibleWith(TabStrip* other) const {
 
 NewTabButtonPosition BrowserTabStripController::GetNewTabButtonPosition()
     const {
-  if (!ui::MaterialDesignController::IsRefreshUi())
+  if (!ui::MaterialDesignController::IsRefreshUi() ||
+      base::FeatureList::IsEnabled(kRefreshNewTabButtonAfterTabs)) {
     return AFTER_TABS;
+  }
   return GetFrameView()->CaptionButtonsOnLeadingEdge() ? TRAILING : LEADING;
 }