chromeos: fix bug in ArcScreenCaptureSession with mash

In SingleProcessMash there are two aura::Envs. See design doc for details.
This code was calling aura::Env::GetInstance() and expecting to get Ash's
Env. In SingleProcessMash aura::Env::GetInstance() returns Chrome's aura::Env.
The fix is to get the env from the window.

I'm also renaming 'desktop_window_' to display_root_window_ to make it clearer
that the window corresponds only to a display root.

BUG=b:124258894
TEST=none

Change-Id: I3b85610d72ada8adb674441e6e47d5ddd9d1b37f
Reviewed-on: https://chromium-review.googlesource.com/c/1483351Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634737}

chrome/browser/chromeos/arc/screen_capture/arc_screen_capture_session.cc

@@ -96,7 +96,6 @@ ArcScreenCaptureSession::ArcScreenCaptureSession(
     : binding_(this),
       notifier_(std::move(notifier)),
       size_(size),
-      desktop_window_(nullptr),
       client_native_pixmap_factory_(
           gfx::CreateClientNativePixmapFactoryDmabuf()),
       weak_ptr_factory_(this) {}
@@ -106,18 +105,19 @@ mojom::ScreenCaptureSessionPtr ArcScreenCaptureSession::Initialize(
     const std::string& display_name,
     bool enable_notification) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  desktop_window_ = content::DesktopMediaID::GetNativeWindowById(desktop_id);
-  if (!desktop_window_) {
+  display_root_window_ =
+      content::DesktopMediaID::GetNativeWindowById(desktop_id);
+  if (!display_root_window_) {
     LOG(ERROR) << "Unable to find Aura desktop window";
     return nullptr;
   }
 
-  ui::Layer* layer = desktop_window_->layer();
+  ui::Layer* layer = display_root_window_->layer();
   if (!layer) {
     LOG(ERROR) << "Unable to find layer for the desktop window";
     return nullptr;
   }
-  auto context_provider = aura::Env::GetInstance()
+  auto context_provider = display_root_window_->env()
                               ->context_factory()
                               ->SharedMainThreadContextProvider();
   gl_helper_ = std::make_unique<viz::GLHelper>(
@@ -129,7 +129,7 @@ mojom::ScreenCaptureSessionPtr ArcScreenCaptureSession::Initialize(
       gfx::Vector2d(desktop_size.width(), desktop_size.height()),
       gfx::Vector2d(size_.width(), size_.height()), false, true, false);
 
-  desktop_window_->GetHost()->compositor()->AddAnimationObserver(this);
+  display_root_window_->GetHost()->compositor()->AddAnimationObserver(this);
 
   if (enable_notification) {
     // Show the tray notification icon now.
@@ -159,7 +159,10 @@ void ArcScreenCaptureSession::Close() {
 }
 
 ArcScreenCaptureSession::~ArcScreenCaptureSession() {
-  desktop_window_->GetHost()->compositor()->RemoveAnimationObserver(this);
+  if (!display_root_window_)
+    return;
+
+  display_root_window_->GetHost()->compositor()->RemoveAnimationObserver(this);
   ash::Shell::Get()->display_manager()->dec_screen_capture_active_counter();
   ash::Shell::Get()->UpdateCursorCompositingEnabled();
 }
@@ -352,7 +355,7 @@ void ArcScreenCaptureSession::OnAnimationStep(base::TimeTicks timestamp) {
     return;
   }
 
-  ui::Layer* layer = desktop_window_->layer();
+  ui::Layer* layer = display_root_window_->layer();
   if (!layer) {
     LOG(ERROR) << "Unable to find layer for the desktop window";
     return;
@@ -363,7 +366,7 @@ void ArcScreenCaptureSession::OnAnimationStep(base::TimeTicks timestamp) {
           base::BindOnce(&ArcScreenCaptureSession::OnDesktopCaptured,
                          weak_ptr_factory_.GetWeakPtr()));
   // Clip the requested area to the desktop area. See b/118675936.
-  request->set_area(gfx::Rect(desktop_window_->bounds().size()));
+  request->set_area(gfx::Rect(display_root_window_->bounds().size()));
   layer->RequestCopyOfOutput(std::move(request));
 }
 

chrome/browser/chromeos/arc/screen_capture/arc_screen_capture_session.h

@@ -93,7 +93,9 @@ class ArcScreenCaptureSession : public mojom::ScreenCaptureSession,
   mojo::Binding<mojom::ScreenCaptureSession> binding_;
   mojom::ScreenCaptureSessionNotifierPtr notifier_;
   gfx::Size size_;
-  aura::Window* desktop_window_;
+  // aura::Window of the display being captured. This corresponds to one of
+  // Ash's root windows.
+  aura::Window* display_root_window_ = nullptr;
 
   // We have 2 separate queues for handling incoming GPU buffers from Android
   // and also textures for the desktop we have captured already. Due to the