cheets: add wallpaper observer to arc_wallpaper_service.

chrome/browser/chromeos/arc/arc_wallpaper_service.cc

Index: chrome/browser/chromeos/arc/arc_wallpaper_service.cc
diff --git a/chrome/browser/chromeos/arc/arc_wallpaper_service.cc b/chrome/browser/chromeos/arc/arc_wallpaper_service.cc
index f6a12cdb5a1eaba07ac09ec039de27a4aba85917..5cb7a9dfd26c3138d964f40471edf3f51c4c7fce 100644
--- a/chrome/browser/chromeos/arc/arc_wallpaper_service.cc
+++ b/chrome/browser/chromeos/arc/arc_wallpaper_service.cc
@@ -31,6 +31,7 @@ namespace arc {
 
 namespace {
 
+constexpr uint32_t kMinOnWallpaperChangedVersion = 1;
 constexpr char kAndroidWallpaperFilename[] = "android.jpg";
 
 // Sets a decoded bitmap as the wallpaper.
@@ -81,6 +82,10 @@ ArcWallpaperService::~ArcWallpaperService() {
   // Make sure the callback is never called after destruction. It is safe to
   // call Cancel() even when there is no in-flight request.
   ImageDecoder::Cancel(this);
+  ash::WmShell* wm_shell = ash::WmShell::Get();
+  if (wm_shell && wm_shell->wallpaper_controller()) {
+    wm_shell->wallpaper_controller()->RemoveObserver(this);
+  }
   arc_bridge_service()->wallpaper()->RemoveObserver(this);
 }
 
@@ -94,6 +99,7 @@ void ArcWallpaperService::OnInstanceReady() {
     return;
   }
   wallpaper_instance->Init(binding_.CreateInterfacePtrAndBind());
+  ash::WmShell::Get()->wallpaper_controller()->AddObserver(this);
 }
 
 void ArcWallpaperService::SetWallpaper(mojo::Array<uint8_t> png_data) {
@@ -122,4 +128,33 @@ void ArcWallpaperService::OnDecodeImageFailed() {
   LOG(ERROR) << "Failed to decode wallpaper image.";
 }
 
+void ArcWallpaperService::OnWallpaperDataChanged() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  mojom::WallpaperInstance* instance =
+      GetWallpaperInstance(kMinOnWallpaperChangedVersion);
+  if (!instance) {
+    ash::WmShell::Get()->wallpaper_controller()->RemoveObserver(this);

[Luis Héctor Chávez, 2016/09/16 19:58:11]

It's better to do this in the OnInstanceClosed() rather than here.

[Muyuan, 2016/09/16 20:19:08]

I see. So here is a question:
Is there a guarantee that Android side will be torn down before CrOS side? In
other words, is OnInstanceClosed() always guaranteed to be called prior to
~ArcWallpaperService()? I'm asking this because if it's true, the removal of
WallpaperObserver in ~ArcWallpaperService() could be moved here.

[Luis Héctor Chávez, 2016/09/16 20:27:37]

There are cases where Android outlives Chrome, but are error cases. I'd rather
have two places where the observer is removed (because the second removal is a
no-op): one in OnInstanceClosed() (for symmetry with OnInstanceReady()) and one
in the destructor (for safety). If you omit the latter, the destructor of the
ObserverList will DCHECK since not all Observers were removed.

[Muyuan, 2016/09/16 20:48:56]

Done.

+    return;
+  }
+  instance->OnWallpaperChanged();
+}
+
+mojom::WallpaperInstance* ArcWallpaperService::GetWallpaperInstance(
+    uint32_t min_version) {
+  uint32_t version = arc_bridge_service()->wallpaper()->version();
+  if (version < min_version) {
+    VLOG(1) << "ARC wallpaper instance is too old. required: " << min_version
+            << ", actual: " << version;
+    return nullptr;
+  }
+
+  mojom::WallpaperInstance* instance =
+      arc_bridge_service()->wallpaper()->instance();
+  if (!instance) {
+    VLOG(2) << "ARC wallpaper instance is not ready.";
+  }
+
+  return instance;
+}
+
 }  // namespace arc