cheets: implement cros side of WallpaperManagerService.

components/arc/set_wallpaper_delegate.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_
 #define COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_
 
 #include <stdint.h>
+#include <vector>
 
-#include <vector>
+#include "base/callback_forward.h"
 
 namespace arc {
 
 // Delegate to allow setting the wallpaper.
 class SetWallpaperDelegate {

[Luis Héctor Chávez, 2016/08/30 22:47:15]

Can you rename it to WallpaperDelegate?

[Luis Héctor Chávez, 2016/08/31 04:25:14]

After an offline discussion, this interface should eventually go away. For now
and for backwards compatibility it should stay as-is, but the intention is that
the responsibilities of the WallpaperHost should be assumed by what now is
called ArcWallpaperHandler (the only implementation of SetWallpaperDelegate),
and eventually ArcIntentHelper will stop having wallpaper-related
responsibilities, at which point this class should disappear.

[hidehiko, 2016/08/31 04:59:53]

Clarification: So the plan is;
- Deprecate IntentHelper::SetWallpaper()
- Switch to use WallpaperHost for SetWallpaper in ARC.
- Remove IntentHelper::SetWallpaper()
- Migrate SetWallpaperDelegate into WalpaperHost implementation.

Am I correct? If so, can we move ArcWallpaperBridge c/b/c/arc and migrate with
ArcWallpaperHandler in this CL, because there is no reason to keep the two
classes separated with the plan, I think?
The migrated class can inherit SetWallpaperDelegate with TODO to remove it at
the moment, so that IntentHelper can proxy from its SetWallpaper.

[Muyuan, 2016/09/01 18:49:08]

Done.

  public:
   virtual ~SetWallpaperDelegate() = default;
 
   // Sets an image represented in JPEG format as the wallpaper.
-  virtual void SetWallpaper(std::vector<uint8_t> jpeg_data) = 0;
+  virtual void SetWallpaper(const std::vector<uint8_t>& jpeg_data) = 0;
+  // Gets current wallpaper encoded in JPEG format.
+  virtual void GetWallpaper(
+      const base::Callback<void(const std::vector<uint8_t>& image)>& callback)
+      const = 0;
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_SET_WALLPAPER_DELEGATE_H_