Makes windowmanager draw non-client area

components/mus/example/wm/non_client_frame_view_impl.cc

+// Copyright 2015 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 "components/mus/example/wm/non_client_frame_view_impl.h"
+
+#include "components/mus/public/cpp/window.h"
+#include "ui/compositor/paint_recorder.h"
+#include "ui/gfx/canvas.h"
+
+NonClientFrameViewImpl::NonClientFrameViewImpl(mus::Window* window)
+    : window_(window) {
+  window_->AddObserver(this);
+}
+
+NonClientFrameViewImpl::~NonClientFrameViewImpl() {
+  if (window_)
+    window_->RemoveObserver(this);
+}
+
+gfx::Rect NonClientFrameViewImpl::GetBoundsForClientView() const {
+  gfx::Rect result(GetLocalBounds());
+  result.Inset(window_->client_area());
+  return result;
+}
+
+void NonClientFrameViewImpl::OnPaint(gfx::Canvas* canvas) {
+  canvas->Save();
+  CustomFrameView::OnPaint(canvas);
+  canvas->Restore();
+
+  // The client app draws the client area. Make ours totally transparent so
+  // we only see the client apps client area.
+  canvas->FillRect(GetBoundsForClientView(), SK_ColorBLACK,
+                   SkXfermode::kSrc_Mode);
+}
+
+void NonClientFrameViewImpl::PaintChildren(const ui::PaintContext& context) {
+  CustomFrameView::PaintChildren(context);
+
+  // The client app draws the client area. Make ours totally transparent so
+  // we only see the client apps client area.
+  ui::PaintRecorder recorder(context, size(), &paint_cache_);
+  recorder.canvas()->FillRect(GetBoundsForClientView(), SK_ColorBLACK,
+                              SkXfermode::kSrc_Mode);
+}
+
+void NonClientFrameViewImpl::OnWindowClientAreaChanged(
+    mus::Window* window,
+    const gfx::Insets& old_client_area) {
+  Layout();
+  SchedulePaint();
+}
+
+void NonClientFrameViewImpl::OnWindowDestroyed(mus::Window* window) {
+  window_->RemoveObserver(this);
+  window_ = nullptr;
+}