cheets: implement cros side of WallpaperManagerService.

chrome/browser/chromeos/arc/arc_wallpaper_handler.cc

Index: chrome/browser/chromeos/arc/arc_wallpaper_handler.cc
diff --git a/chrome/browser/chromeos/arc/arc_wallpaper_handler.cc b/chrome/browser/chromeos/arc/arc_wallpaper_handler.cc
index 238a9837e121ffe019e3e1076c9429b7ff177420..b32c4c7ad90469639ad8614a994dee60982ee57f 100644
--- a/chrome/browser/chromeos/arc/arc_wallpaper_handler.cc
+++ b/chrome/browser/chromeos/arc/arc_wallpaper_handler.cc
@@ -8,6 +8,9 @@
 #include <utility>
 #include <vector>
 
+#include "ash/desktop_background/desktop_background_controller.h"
+#include "ash/shell.h"
+#include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h"
@@ -16,7 +19,9 @@
 #include "components/wallpaper/wallpaper_files_id.h"
 #include "components/wallpaper/wallpaper_layout.h"
 #include "content/public/browser/browser_thread.h"
+#include "ui/gfx/image/image.h"
 #include "ui/gfx/image/image_skia.h"
+#include "ui/gfx/image/image_util.h"
 
 using user_manager::UserManager;
 
@@ -56,6 +61,14 @@ void SetBitmapAsWallpaper(const SkBitmap& bitmap) {
   // wallpaper_private_api.cc.
 }
 
+void EncodeImageJPEG(
+    const gfx::Image image,
+    const base::Callback<void(std::vector<uint8_t> result)>& callback) {
+  std::vector<uint8_t> result;
+  gfx::JPEG1xEncodedDataFromImage(image, 100, &result);
+  callback.Run(result);

[Shuhei Takahashi, 2016/08/23 09:34:21]

We must invoke |callback| on UI thread. Please use PostTaskAndReply() to bounce
back to UI thread.

Also please make sure to use std::move() where possible to reduce copies. Note
that, as lhchavez@ pointed out in earlier comment, you should not use
std::move() when returning a local variable nevertheless.

[Muyuan, 2016/08/23 19:45:49]

Acknowledged.

+}
+
 }  // namespace
 
 ArcWallpaperHandler::ArcWallpaperHandler() = default;
@@ -76,6 +89,17 @@ void ArcWallpaperHandler::SetWallpaper(std::vector<uint8_t> jpeg_data) {
                                  ImageDecoder::ROBUST_JPEG_CODEC, true);
 }
 
+void ArcWallpaperHandler::GetWallpaper(
+    const base::Callback<void(std::vector<uint8_t> image)>& callback) const {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  ash::DesktopBackgroundController* dbc =
+      ash::Shell::GetInstance()->desktop_background_controller();
+  gfx::Image wallpaper(dbc->GetWallpaper());

[Shuhei Takahashi, 2016/08/23 09:34:21]

I know gfx::JPEG1xEncodedDataFromImage() actually checks if a given image is
null, but could you check it by yourself explicitly?

Documentation of gfx::JPEG1xEncodedDataFromImage() does not mention about the
behavior when a null image is given:
https://cs.chromium.org/chromium/src/ui/gfx/image/image_util.h?sq=package:chr...

OTOH, documentation of gfx::Image warns that use of a null image will cause a
crash:
https://cs.chromium.org/chromium/src/ui/gfx/image/image.h?q=gfx::image&sq=pac...

[Muyuan, 2016/08/23 19:45:49]

DesktopBackgroundController::GetWallpaper() will return an empty image when the
background is not available so it should not be null.

+  content::BrowserThread::PostTask(
+      content::BrowserThread::IO, FROM_HERE,

[xiyuan, 2016/08/22 22:49:41]

IO thread is for network IO etc. Maybe do the job in a blocking pool thread?

[Muyuan, 2016/08/22 23:48:19]

Acknowledged.

[Shuhei Takahashi, 2016/08/23 09:34:21]

As xiyuan said, please avoid doing CPU-intensive task on IO thread. For example
message loop of IPC between browser and renderer is performed on this thread, so
during JPEG decoding, IPC will be choked.

[Muyuan, 2016/08/23 19:45:49]

Acknowledged.

+      base::Bind(&EncodeImageJPEG, wallpaper, callback));
+}
+
 void ArcWallpaperHandler::OnImageDecoded(const SkBitmap& bitmap) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   SetBitmapAsWallpaper(bitmap);