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

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

Index: chrome/browser/ui/views/toolbar/back_button.cc
diff --git a/chrome/browser/ui/views/toolbar/back_button.cc b/chrome/browser/ui/views/toolbar/back_button.cc
index f713da2bd9f9f282a2956b02666bf354a6b2f286..8a03cd31f29fe0ccf675d8f47e72ed61c4c7f7f3 100644
--- a/chrome/browser/ui/views/toolbar/back_button.cc
+++ b/chrome/browser/ui/views/toolbar/back_button.cc
@@ -21,11 +21,13 @@ void BackButton::SetLeadingMargin(int 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();
 }