Don't use dashed focus painter on back button in MD mode.

chrome/browser/ui/views/toolbar/back_button.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/toolbar/back_button.h"
 
 #include "ui/gfx/geometry/insets.h"
 #include "ui/views/animation/ink_drop.h"
 #include "ui/views/controls/button/label_button_border.h"
 #include "ui/views/painter.h"
 
 BackButton::BackButton(Profile* profile,
                        views::ButtonListener* listener,
                        ui::MenuModel* model)
     : ToolbarButton(profile, listener, model), margin_leading_(0) {}
 
 BackButton::~BackButton() {}
 
 void BackButton::SetLeadingMargin(int margin) {
   margin_leading_ = margin;
 
   UpdateThemedBorder();
 
-  const int inset = LabelButton::kFocusRectInset;
-  const bool is_rtl = base::i18n::IsRTL();
-  const gfx::Insets insets(inset, inset + (is_rtl ? 0 : margin),
-                           inset, inset + (is_rtl ? margin : 0));
-  SetFocusPainter(views::Painter::CreateDashedFocusPainterWithInsets(insets));
+  if (focus_painter()) {

[Peter Kasting, 2016/06/14 17:51:59]

Who would be setting this?  It reads here a bit like "if there's a focus
painter, set a focus painter" which sounds circular.  Should this have a comment
on how the focus painter would get set here?

[Evan Stade, 2016/06/14 17:57:34]

ToolbarButton (the parent class). In my head it reads as, "If there's supposed
to be a focus painter, give it special insets. If there's no focus painter,
don't add one."

[Peter Kasting, 2016/06/14 18:00:21]

Does ToolbarButton ever add such a focus painter?  It seems like giving
accessibility focus to the button doesn't do this in MD, so I'm wondering if we
should just nuke the focus painter code here entirely, or maybe make it pre-MD
only.

+    const int inset = LabelButton::kFocusRectInset;
+    const bool is_rtl = base::i18n::IsRTL();
+    const gfx::Insets insets(inset, inset + (is_rtl ? 0 : margin),
+                             inset, inset + (is_rtl ? margin : 0));
+    SetFocusPainter(views::Painter::CreateDashedFocusPainterWithInsets(insets));
+  }
   InvalidateLayout();
 }
 
 const char* BackButton::GetClassName() const {
   return "BackButton";
 }
 
 std::unique_ptr<views::LabelButtonBorder> BackButton::CreateDefaultBorder()
     const {
   std::unique_ptr<views::LabelButtonBorder> border =
       ToolbarButton::CreateDefaultBorder();
 
   // Adjust border insets to follow the margin change,
   // which will be reflected in where the border is painted
   // through GetThemePaintRect().
   const gfx::Insets insets(border->GetInsets());
   border->set_insets(gfx::Insets(insets.top(), insets.left() + margin_leading_,
                                  insets.bottom(), insets.right()));
 
   return border;
 }
 
 gfx::Rect BackButton::GetThemePaintRect() const {
   gfx::Rect rect(LabelButton::GetThemePaintRect());
   const bool is_rtl = base::i18n::IsRTL();
   rect.Inset(is_rtl ? 0 : margin_leading_, 0, is_rtl ? margin_leading_ : 0, 0);
   return rect;
 }