views: wires up IsActive() for DesktopWindowTreeHostPlatform

BUG=none
TEST=none

Change-Id: Iaa61d9eeb3813e5d8131c0790693b69e73fe9602
Reviewed-on: https://chromium-review.googlesource.com/998496Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548585}

ui/views/widget/desktop_aura/desktop_window_tree_host_platform.cc

@@ -241,9 +241,7 @@ void DesktopWindowTreeHostPlatform::Deactivate() {
 }
 
 bool DesktopWindowTreeHostPlatform::IsActive() const {
-  // TODO: needs PlatformWindow support.
-  NOTIMPLEMENTED_LOG_ONCE();
-  return false;
+  return is_active_;
 }
 
 void DesktopWindowTreeHostPlatform::Maximize() {
@@ -416,6 +414,7 @@ void DesktopWindowTreeHostPlatform::OnCloseRequest() {
 }
 
 void DesktopWindowTreeHostPlatform::OnActivationChanged(bool active) {
+  is_active_ = active;
   aura::WindowTreeHostPlatform::OnActivationChanged(active);
   desktop_native_widget_aura_->HandleActivationChanged(active);
 }

ui/views/widget/desktop_aura/desktop_window_tree_host_platform.h

@@ -104,6 +104,8 @@ class VIEWS_EXPORT DesktopWindowTreeHostPlatform
 
   bool got_on_closed_ = false;
 
+  bool is_active_ = false;
+
   base::WeakPtrFactory<DesktopWindowTreeHostPlatform> weak_factory_{this};
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostPlatform);