Monitor the system native frame color on Win 10.

chrome/browser/themes/theme_service_win.cc

+// 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.
+
+#include "chrome/browser/themes/theme_service_win.h"
+
+#include "base/bind.h"
+#include "base/win/windows_version.h"
+#include "chrome/browser/themes/theme_properties.h"
+#include "grit/theme_resources.h"
+#include "skia/ext/skia_utils_win.h"
+#include "ui/base/win/shell.h"
+
+ThemeServiceWin::ThemeServiceWin() {

[Evan Stade, 2016/03/03 01:24:25]

init dwm_frame_color_?

[Peter Kasting, 2016/03/03 09:23:06]

There's no need, since the code in the conditional here is guaranteed to
initialize it in a superset of the cases where we read it.

[Evan Stade, 2016/03/03 18:17:19]

yes, but we run static analysis tools that don't know that so I think the
general policy is to always init PODs

+  // This just checks for Windows 10 instead of calling ShouldUseDwmFrameColor()
+  // because we want to monitor the frame color even when a custom frame is in
+  // use, so that it will be correct if at any time the user switches to the
+  // native frame.
+  if (base::win::GetVersion() >= base::win::VERSION_WIN10) {
+    dwm_key_.reset(new base::win::RegKey(
+        HKEY_CURRENT_USER, L"SOFTWARE\\Microsoft\\Windows\\DWM", KEY_READ));
+    OnDwmKeyUpdated();
+  }
+}
+
+ThemeServiceWin::~ThemeServiceWin() {
+}
+
+bool ThemeServiceWin::ShouldUseNativeFrame() const {
+  return !HasCustomImage(IDR_THEME_FRAME) && ui::win::IsAeroGlassEnabled();
+}
+
+SkColor ThemeServiceWin::GetDefaultColor(int id, bool incognito) const {
+  if (ShouldUseDwmFrameColor()) {
+    switch (id) {
+      // Active native windows on Windows 10 may have a custom frame color.
+      case ThemeProperties::COLOR_FRAME:

[Bret, 2016/03/02 22:54:03]

i still think "frame" is a confusing name for this color even after you
explained the context. we might not even use it for the frame

[Peter Kasting, 2016/03/03 09:23:06]

I understand where you're coming from.

That said, the "frame" in Chrome UI code refers to e.g. the opaque frame, glass
frame, etc.  I think it's reasonable in principle for us to refer to the primary
color of the UI drawn by those classes as the "frame color".

Much more importantly, this is terminology that's used in a number of different
places, including e.g. themes where it's externally exposed by the same name
(theme authors set the "frame" color in their themes, and similar names for
related colors).  We can't modify these externally-facing strings (at least
without extraordinary measures).  Accordingly, changing this name would make the
connection to themes confusing, and that connection is arguably the most
important thing in how we name these constants.

+      case ThemeProperties::COLOR_FRAME_INCOGNITO:

[Evan Stade, 2016/03/03 01:24:25]

I don't think you can hit this (or the other incognito one below). You'd get
COLOR_FRAME with incognito == true instead, although you don't care about
incognito's value in this case.

[Peter Kasting, 2016/03/03 09:23:06]

You're right.  I misread the original code before I factored this out. 
Simplified.

+        return dwm_frame_color_;
+
+      // Inactive native windows on Windows 10 always have a white frame.
+      case ThemeProperties::COLOR_FRAME_INACTIVE:
+      case ThemeProperties::COLOR_FRAME_INCOGNITO_INACTIVE:
+        return SK_ColorWHITE;
+    }
+  }
+
+  return ThemeService::GetDefaultColor(id, incognito);
+}
+
+bool ThemeServiceWin::ShouldUseDwmFrameColor() const {
+  return ShouldUseNativeFrame() &&
+         (base::win::GetVersion() >= base::win::VERSION_WIN10);
+}
+
+void ThemeServiceWin::OnDwmKeyUpdated() {
+  // Attempt to read the accent color.
+  DWORD accent_color, color_prevalence;
+  dwm_frame_color_ =
+      ((dwm_key_->ReadValueDW(L"ColorPrevalence", &color_prevalence) ==
+        ERROR_SUCCESS) &&
+       (color_prevalence == 1) &&
+       (dwm_key_->ReadValueDW(L"AccentColor", &accent_color) == ERROR_SUCCESS))
+          ? skia::COLORREFToSkColor(accent_color)
+          : SK_ColorWHITE;
+
+  // Watch for future changes.
+  if (!dwm_key_->StartWatching(base::Bind(
+          &ThemeServiceWin::OnDwmKeyUpdated, base::Unretained(this))))
+    dwm_key_.reset();
+}