Extract colors from wallpaper and dynamically update login screen overlay

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc

Index: chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
diff --git a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
index 675f657833b61b87a09e1b6a674d56bc97d0d1ac..5b75149a36ef66592d037aec74c1cb808c93f116 100644
--- a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
+++ b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
@@ -204,6 +204,7 @@ void SetKnownUserWallpaperFilesId(
 // A helper to set the wallpaper image for Classic Ash and Mash.
 void SetWallpaper(const gfx::ImageSkia& image,
                   wallpaper::WallpaperLayout layout) {
+  WallpaperManager::Get()->CalculateProminentColor(image);
   if (ash_util::IsRunningInMash()) {
     // In mash, connect to the WallpaperController interface via mojo.
     service_manager::Connector* connector =
@@ -427,6 +428,22 @@ bool WallpaperManager::IsPendingWallpaper(uint32_t image_id) {
   return false;
 }
 
+void WallpaperManager::CalculateProminentColor(const gfx::ImageSkia& image) {
+  if (color_calculator_) {
+    color_calculator_->RemoveObserver(this);

[jdufault, 2017/06/12 21:37:28]

Add a comment along the lines of 

  // Cancel any in-flight color calculations

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Done.

+    color_calculator_.reset();
+  }
+
+  color_utils::LumaRange luma = color_utils::LumaRange::DARK;

[jdufault, 2017/06/12 21:37:28]

Eliminate the |luma| and |saturation| temporaries. They don't provide additional
semantic value and the typing reduction is minimal.

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Done.

+  color_utils::SaturationRange saturation = color_utils::SaturationRange::MUTED;
+
+  color_calculator_ = base::MakeUnique<wallpaper::WallpaperColorCalculator>(
+      image, luma, saturation, task_runner_);
+  color_calculator_->AddObserver(this);
+  if (!color_calculator_->StartCalculation())
+    SetProminentColor(SK_ColorTRANSPARENT);
+}
+
 WallpaperManager::WallpaperResolution
 WallpaperManager::GetAppropriateResolution() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
@@ -911,6 +928,12 @@ void WallpaperManager::OnWindowDestroying(aura::Window* window) {
       user_manager::UserManager::Get()->GetActiveUser()->username_hash());
 }
 
+void WallpaperManager::OnColorCalculationComplete() {
+  const SkColor color = color_calculator_->prominent_color();
+  color_calculator_.reset();

[jdufault, 2017/06/12 21:37:28]

Add a comment explaining why you cache color instead of just using
color_calculator_->prominent_color() directly, ie,

  SetProminentColor(color_calculator_->prominent_color());
  color_calculator_.reset().

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Changed to using the color directly.

+  SetProminentColor(color);
+}
+
 // WallpaperManager, private: --------------------------------------------------
 
 WallpaperManager::WallpaperManager()
@@ -1105,6 +1128,15 @@ void WallpaperManager::OnDeviceWallpaperDecoded(
       ->ResetSetWallpaperImage(user_image->image(), wallpaper_info);
 }
 
+void WallpaperManager::SetProminentColor(SkColor color) {
+  if (prominent_color_ == color)
+    return;
+
+  prominent_color_ = color;
+  for (auto& observer : observers_)
+    observer.OnColorCalculationComplete();
+}
+
 void WallpaperManager::InitializeRegisteredDeviceWallpaper() {
   if (user_manager::UserManager::Get()->IsUserLoggedIn())
     return;