[Download Home] Add image thumbnail support

chrome/browser/android/download/ui/thumbnail_provider.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 CHROME_BROWSER_ANDROID_DOWNLOAD_UI_THUMBNAIL_PROVIDER_H_
+#define CHROME_BROWSER_ANDROID_DOWNLOAD_UI_THUMBNAIL_PROVIDER_H_
+
+#include <string>
+
+#include "base/android/jni_android.h"
+#include "chrome/browser/image_decoder.h"
+
+// Kicks off asynchronous pipelines for creating thumbnails for local files.
+// The native-side ThumbnailProvider is owned by the Java-side and can be

[Ian Wen, 2016/08/31 00:08:10]

nit: simplify the comments to be "This class is owned by the java-side
counterpart"?

[gone, 2016/08/31 01:35:04]

Wanted to be explicitly clear about how the ImageRequests are handled inside the
CC part of the file.  Those are fired to the ImageDecoder and its utility
process and manage their own lifecycles, even if this class is destroyed.

+// safely destroyed while a request is being processed.
+class ThumbnailProvider {
+ public:
+  ThumbnailProvider(const base::android::JavaParamRef<jobject>& jobj,
+                    int icon_size);
+
+  // Destroys the ThumbnailProvider.  Any currently running ImageRequest will
+  // delete itself when it has completed.
+  void Destroy(JNIEnv* env,
+               const base::android::JavaParamRef<jobject>& jobj);
+
+  // Kicks off an asynchronous process to retrieve the thumbnail for the file
+  // located at |file_path| with a max size of |icon_size| in each dimension.
+  void RetrieveThumbnail(JNIEnv* env,
+                         const base::android::JavaParamRef<jobject>& jobj,
+                         jstring file_path,
+                         jint icon_size);
+
+  // Called when the thumbnail is ready.  |thumbnail| will be empty on failure.
+  void OnThumbnailRetrieved(const std::string& file_path,
+                            const SkBitmap& thumbnail);
+
+  // Registers the JNI bindings.
+  static bool RegisterJNI(JNIEnv* env);
+
+ private:
+  ~ThumbnailProvider();
+
+  base::android::ScopedJavaGlobalRef<jobject> java_delegate_;
+  base::WeakPtrFactory<ThumbnailProvider> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThumbnailProvider);
+};
+
+#endif  // CHROME_BROWSER_ANDROID_DOWNLOAD_UI_THUMBNAIL_PROVIDER_H_