Draw infobar arrow border with width of 1px on any scale factor.

chrome/browser/ui/views/infobars/infobar_view.cc

Index: chrome/browser/ui/views/infobars/infobar_view.cc
diff --git a/chrome/browser/ui/views/infobars/infobar_view.cc b/chrome/browser/ui/views/infobars/infobar_view.cc
index b0012dc05b02af4bc2c6072ce4d2f8a461c50246..ff4a7cf84d25f663c9cf705287c2ff927a7cc6c3 100644
--- a/chrome/browser/ui/views/infobars/infobar_view.cc
+++ b/chrome/browser/ui/views/infobars/infobar_view.cc
@@ -200,9 +200,6 @@ void InfoBarView::Layout() {
       stroke_path_.rLineTo(arrow_fill_half_width, arrow_fill_height);

[Peter Kasting, 2016/03/22 23:39:18]

I don't think this code is technically correct in non-1x scales, because e.g.
the half-pixel offset will get scaled to one pixel and we'll wind up with a path
whose coordinate is no longer in the pixel center.

I think what we need to do here is the same sort of thing I do for the tab
outlines: we need to make a path that assumes it will be drawn unscaled, then at
the drawing site we need to unscale and draw the path.

As a side effect this will also mean we can avoid hairlines since we'll always
be drawing unscaled and can just use a 1 px thickness.

 
       fill_path_ = stroke_path_;
-      // Move the top of the fill path up to the top of the separator and then
-      // extend it down all the way through.
-      fill_path_.offset(0, -separator_height * SK_ScalarHalf);
       // This 0.01 hack prevents the fill from filling more pixels on the right
       // edge of the arrow than on the left.

[Peter Kasting, 2016/03/22 23:39:18]

Now that I know more about Skia than when I wrote this, the right way to compute
the fill is probably the way we do it for the MD tabstrip: start with the same
path as the stroke, but then use Op() from SkPathOps.h to subtract the stroked
stroke path away.  This would avoid the need for an epsilon like this.

       const SkScalar epsilon = 0.01f;
@@ -213,10 +210,8 @@ void InfoBarView::Layout() {
     }
   }
   if (bar_height()) {
-    fill_path_.addRect(
-        0.0, SkIntToScalar(arrow_height()), SkIntToScalar(width()),
-        SkIntToScalar(
-            height() - InfoBarContainerDelegate::kSeparatorLineHeight));
+    fill_path_.addRect(0.0, SkIntToScalar(arrow_height()),
+                       SkIntToScalar(width()), SkIntToScalar(height()));
   }
 
   child_container_->SetBounds(