Have Chrome draw top window border when using custom titlebar.

chrome/browser/ui/views/frame/glass_browser_frame_view.cc

Index: chrome/browser/ui/views/frame/glass_browser_frame_view.cc
diff --git a/chrome/browser/ui/views/frame/glass_browser_frame_view.cc b/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
index 98d1063b2ea1f5353d5ccd642c28927d41fbee11..ab6dc571ebd138efb9768bdacdc7d7c7ba325064 100644
--- a/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
+++ b/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
@@ -509,14 +509,38 @@ void GlassBrowserFrameView::PaintTitlebar(gfx::Canvas* canvas) const {
   // BrowserDesktopWindowTreeHostWin::UpdateDWMFrame()).
   const int y = IsMaximized() ? FrameTopBorderThicknessPx(false) : 1;
   SkPaint paint;
+
+  // Draw the top of the accent border.
+  //
+  // We let the DWM do this for the other sides of the window by insetting the
+  // client area to leave nonclient area available. However, along the top
+  // window edge, we have to have zero nonclient area or the DWM will draw a
+  // full native titlebar outside our client area. See
+  // BrowserDesktopWindowTreeHostWin::GetClientAreaInsets().
+  //
+  // We could ask the DWM to draw the top accent border in the client area (by
+  // calling DwmExtendFrameIntoClientArea in

[Peter Kasting, 2016/10/11 20:01:38]

Nit: Add () after function name

+  // BrowserDesktopWindowTreeHostWin::UpdateDWMFrame()), but this requires
+  // that we leave part of the client surface transparent. Forcing DWM to
+  // blend with us costs power even when it has no effect. If we draw this

[Peter Kasting, 2016/10/11 20:01:38]

Nit: What does "even when it has no effect" mean here?  Are you describing the
maximized window case?

I would probably just leave this clause out as it's not really clear in context
what it means.  If you want to leave it, maybe make it clearer: "costs power
(even if the accent border area winds up offscreen, e.g. for a maximized
window)."

+  // ourselves, we can make the client surface fully opaque and avoid this
+  // cost.
+  //
+  // So the accent border also has to be opaque, but native inactive borders
+  // are #565656 with 80% alpha. We copy Edge (which also custom-draws its top
+  // border) and use #A2A2A2 instead.
+  // TODO(jbauman): Match Edge's #090909 when using the dark theme.

[Peter Kasting, 2016/10/11 20:01:38]

Which dark theme are you referring to?  Chrome incognito?  Something in Windows?

[Bret, 2016/10/11 20:48:19]

In Edge it's a user setting, but that's just because it doesn't respect the
frame color at all. I imagine we'd do it in the same cases where we'd want to
draw dark-themed caption buttons (but we haven't decided on those cases yet).

[Peter Kasting, 2016/10/11 20:56:51]

I see.

I use a dark frame color on my own system and the 0xA2 inactive accent border
still seems reasonable, so my suspicion is that we may not ever want this,
though I'm not sure.

I might omit this comment for now if we don't know if/when we'll be doing this,
especially if we didn't also change the other three accent borders to be opaque
at the same time, since it'd look pretty weird.

[Bret, 2016/10/11 21:10:15]

I think it's somewhere between extremely difficult and impossible to custom-draw
the other borders so they're opaque. I'm okay having it be A2 even in the dark
theme case; it does look a little strange when Edge does it.

+  constexpr SkColor inactive_border_color = 0xFFA2A2A2;
+  paint.setColor(
+      ShouldPaintAsActive()
+          ? GetThemeProvider()->GetColor(ThemeProperties::COLOR_ACCENT_BORDER)
+          : inactive_border_color);
+  canvas->DrawRect(gfx::RectF(0, 0, width() * scale, y), paint);
+
   paint.setColor(frame_color);
   canvas->DrawRect(
       gfx::RectF(0, y, width() * scale, tabstrip_bounds.bottom() * scale - y),
       paint);
-
-  // The 1 pixel line at the top is drawn by Windows when we leave that section
-  // of the window blank because we have called DwmExtendFrameIntoClientArea()
-  // inside BrowserDesktopWindowTreeHostWin::UpdateDWMFrame().
 }
 
 void GlassBrowserFrameView::PaintToolbarBackground(gfx::Canvas* canvas) const {