Make image_decoder a Leaky LazyInstance

chrome/browser/image_batch_decoder.h

+// Copyright (c) 2015 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 CHROME_BROWSER_IMAGE_BATCH_DECODER_H_
+#define CHROME_BROWSER_IMAGE_BATCH_DECODER_H_
+
+#include <map>
+#include <string>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/compiler_specific.h"
+#include "base/memory/ref_counted.h"
+#include "base/threading/sequenced_worker_pool.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/utility_process_host.h"
+#include "content/public/browser/utility_process_host_client.h"
+
+using content::UtilityProcessHost;
+using content::BrowserThread;
+
+class SkBitmap;
+
+// Decodes images in a sandboxed process. Reuses a single UtilityProcessHost
+// in batch mode to facilitate decoding multiple images.
+class ImageBatchDecoder : public content::UtilityProcessHostClient {
+ public:
+  class Delegate {
+   public:
+    // Called when image is decoded.
+    // |decoder| is used to identify the image in case of decoding several
+    // images simultaneously.
+    virtual void OnImageDecoded(const ImageBatchDecoder* decoder,
+                                const SkBitmap& decoded_image) = 0;
+
+    // Called when decoding image failed. Delegate can do some cleanup in
+    // this handler.
+    virtual void OnDecodeImageFailed(const ImageBatchDecoder* decoder) {}
+
+   protected:
+    virtual ~Delegate() {}
+  };
+
+  enum ImageCodec {
+    DEFAULT_CODEC = 0,  // Uses WebKit image decoding (via WebImage).
+    ROBUST_JPEG_CODEC,  // Restrict decoding to robust jpeg codec.
+  };
+
+  // Constructs an ImageBatchDecoder. Callbacks for decoded images wil be
+  // posted back to |task_runner|.
+  explicit ImageBatchDecoder(
+      scoped_refptr<base::SequencedTaskRunner> task_runner);
+
+  // Starts asynchronous image decoding. Once finished, the callback will be
+  // posted back to |task_runner|.
+  void Start(
+             Delegate* delegate,
+             const std::string& image_data,
+             ImageCodec image_codec);
+
+ private:
+  // It's a reference counted object, so destructor is private.
+  ~ImageBatchDecoder() override;
+
+  // Creates a UtilityProcessHost and starts it in batch mode.
+  void ConstructUtilityProcessHost();
+
+  // Overidden from UtilityProcessHostClient:
+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  // IPC message handlers.
+  void OnDecodeImageSucceeded(const SkBitmap& decoded_image, int id);
+  void OnDecodeImageFailed(int id);
+
+  // Launches sandboxed process that will decode the image.
+  void DecodeImageInSandbox(Delegate* delegate,
+                            const std::vector<unsigned char>& image_data,
+                            ImageCodec image_codec);
+
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  int id_counter_ = 0;
+  std::map<int, Delegate*> delegate_map_;
+  content::UtilityProcessHost* utility_process_host_;
+
+  DISALLOW_COPY_AND_ASSIGN(ImageBatchDecoder);
+};
+
+#endif  // CHROME_BROWSER_IMAGE_BATCH_DECODER_H_