Change Aura overlay scrollbars from solid color to painted scrollbars.

ui/native_theme/material_design_constants.h

+// Copyright 2016 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.
+
+#ifndef UI_NATIVE_THEME_MATERIAL_DESIGN_CONSTANTS_H_
+#define UI_NATIVE_THEME_MATERIAL_DESIGN_CONSTANTS_H_

[Peter Kasting, 2016/10/17 19:10:24]

You've named this file like it's a general-purpose set of constants, but these
all have to do with scrollbars.  Why not some kind of scrollbar_constants.h? 
I'd rather not tempt people in the future to create a sprawling file with
thousands of general-purpose UI constants in it.  See also next comment.

Honestly, I'd prefer not to have a separate file for constants at all, and just
define these in some other pre-existing header that has to do with scrollbars,
but perhaps that is not feasible.  If possible, though, it would be nice to at
least not put here anything that is only needed in one place -- for example, if
separate individual files handle things like painting (color, alpha), layout
(length, width), and animation (fade durations), I would keep these constants
separately scoped to those files.

[bokan, 2016/10/17 23:21:03]

Ok, I've renamed the file to overlay_scrollbar_constants_aura.h and moved the
painting related properties into native_theme_aura.cc. Unfortunately, the
animation constants will be needed in both Blink and CC so I've kept them here. 

+
+#include "ui/gfx/skia_util.h"
+
+namespace ui {
+
+const SkAlpha kMDScrollbarAlphaNormal = 0x4D;

[Peter Kasting, 2016/10/17 19:10:24]

Why do the file name and these constant names all explicitly refer to material
design?  Now that we've shipped MD top chrome we're actively trying to remove
references to "material" as this is just The Way We Do Things and needs no
special name.  Are you trying to distinguish from some parallel set of non-MD
scrollbar constants?  Isn't the distinction here really "overlay vs.
non-overlay" rather than "MD vs. non-MD"?

So in general I'd prefer to avoid any reference to material/MD in names.

Also: All these should be constexpr.

[bokan, 2016/10/17 23:21:03]

Done.
Done except for SkColorSetRGB which isn't constexpr.

+const SkAlpha kMDScrollbarAlphaHovered = 0x80;
+const SkAlpha kMDScrollbarAlphaPressed = 0x80;
+
+const SkColor kMDScrollbarThumbColor = SkColorSetRGB(0x0, 0x0, 0x0);
+
+const SkColor kMDScrollbarStrokeColor = SkColorSetRGB(0xFF, 0xFF, 0xFF);
+const int kMDScrollbarStrokeWidth = 1;
+
+const int kMDScrollbarThumbWidthNormal = 6;
+const int kMDScrollbarThumbWidthHovered = 10;
+const int kMDScrollbarThumbWidthPressed = 10;
+
+const int kMDScrollbarFadeOutDelayMs = 1000;
+const int kMDScrollbarFadeOutDurationMs = 200;
+
+// TODO(bokan): This is still undetermined. crbug.com/652520.
+const int kMDScrollbarThinningDurationMs = 200;
+
+const int kMDScrollbarMinimumLength = 12;
+
+} // namespace ui
+
+#endif // UI_NATIVE_THEME_MATERIAL_DESIGN_CONSTANTS_H_