Get rid of the huge delay in background resize during rotation

The delay to start updating the wallpaper after rotating the screen used
to be 2 seconds which was also accompanied by unnecessary clearing of
the wallpaper cache resulting in an ugly visual effect.

Now we reduced the delay to only 100 ms and we only clear the cache when
we add another display.

BUG=359654
TEST=manual

Review URL: https://codereview.chromium.org/1131243006

Cr-Commit-Position: refs/heads/master@{#329507}

ash/desktop_background/desktop_background_controller.cc

@@ -45,7 +45,7 @@ namespace {
 
 // How long to wait reloading the wallpaper after the max display has
 // changed?
-const int kWallpaperReloadDelayMs = 2000;
+const int kWallpaperReloadDelayMs = 100;
 
 }  // namespace
 
@@ -136,8 +136,8 @@ void DesktopBackgroundController::OnDisplayConfigurationChanged() {
       timer_.Stop();
       timer_.Start(FROM_HERE,
                    base::TimeDelta::FromMilliseconds(wallpaper_reload_delay_),
-                   this,
-                   &DesktopBackgroundController::UpdateWallpaper);
+                   base::Bind(&DesktopBackgroundController::UpdateWallpaper,
+                              base::Unretained(this), false /* clear cache */));
     }
   }
 }
@@ -153,7 +153,7 @@ void DesktopBackgroundController::OnRootWindowAdded(aura::Window* root_window) {
     current_max_display_size_ = max_display_size;
     if (desktop_background_mode_ == BACKGROUND_IMAGE &&
         current_wallpaper_.get())
-      UpdateWallpaper();
+      UpdateWallpaper(true /* clear cache */);
   }
 
   InstallDesktopController(root_window);
@@ -275,10 +275,10 @@ int DesktopBackgroundController::GetBackgroundContainerId(bool locked) {
                 : kShellWindowId_DesktopBackgroundContainer;
 }
 
-void DesktopBackgroundController::UpdateWallpaper() {
+void DesktopBackgroundController::UpdateWallpaper(bool clear_cache) {
   current_wallpaper_.reset(NULL);
-  ash::Shell::GetInstance()->user_wallpaper_delegate()->
-      UpdateWallpaper(true /* clear cache */);
+  ash::Shell::GetInstance()->user_wallpaper_delegate()->UpdateWallpaper(
+      clear_cache);
 }
 
 }  // namespace ash

ash/desktop_background/desktop_background_controller.h

@@ -133,8 +133,9 @@ class ASH_EXPORT DesktopBackgroundController
   // Send notification that background animation finished.
   void NotifyAnimationFinished();
 
-  // Reload the wallpaper.
-  void UpdateWallpaper();
+  // Reload the wallpaper. |clear_cache| specifies whether to clear the
+  // wallpaper cahce or not.
+  void UpdateWallpaper(bool clear_cache);
 
   void set_wallpaper_reload_delay_for_test(bool value) {
     wallpaper_reload_delay_ = value;