Implement manifest icon downloader

chrome/browser/manifest/manifest_icon_downloader.cc

+// Copyright 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.
+
+#include "chrome/browser/manifest/manifest_icon_downloader.h"
+
+#include "chrome/browser/manifest/manifest_icon_selector.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/web_contents.h"
+#include "skia/ext/image_operations.h"
+#include "ui/gfx/screen.h"
+
+bool ManifestIconDownloader::Download(
+    content::WebContents* web_contents,
+    const GURL& icon_url,
+    int ideal_icon_size_in_dp,
+    const ManifestIconDownloader::IconFetchCallback& callback) {
+  if (!web_contents || !icon_url.is_valid()) return false;
+
+  const gfx::Screen* screen =
+      gfx::Screen::GetScreenFor(web_contents->GetNativeView());
+  const float device_scale_factor =
+      screen->GetPrimaryDisplay().device_scale_factor();
+  const float ideal_icon_size_in_px =
+      ideal_icon_size_in_dp * device_scale_factor;
+
+  web_contents->DownloadImage(
+      icon_url,
+      false, // is_favicon
+      0,     // max_bitmap_size - 0 means no maximum size.
+      false, // bypass_cache
+      base::Bind(&ManifestIconDownloader::OnIconFetched,
+                 ideal_icon_size_in_px,
+                 callback));
+  return true;
+}
+
+void ManifestIconDownloader::OnIconFetched(
+    int ideal_icon_size_in_px,
+    const ManifestIconDownloader::IconFetchCallback& callback,
+    int id,
+    int http_status_code,
+    const GURL& url,
+    const std::vector<SkBitmap>& bitmaps,
+    const std::vector<gfx::Size>& sizes) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  const int closest_index = FindClosestBitmapIndex(
+      ideal_icon_size_in_px, bitmaps);
+
+  if (closest_index == -1) {
+    callback.Run(SkBitmap());
+    return;
+  }
+
+  const SkBitmap& chosen = bitmaps[closest_index];
+
+  // Only scale if we need to scale down. For scaling up we will let the system

[gone, 2015/08/19 22:21:07]

Given that FindClosestBitmapIndex() only returns bitmaps >= the ideal size, in
what situation will we ever have to scale up?

[Lalit Maganti, 2015/08/20 16:48:00]

Ah the algortihm doesn't take into account minimum size restrictions. :/
ideal_icon_size_in_px should probably be minimum_icon_size_in_px in the
algorithm.

+  // handle that when it is required to display it. This saves space in the
+  // webapp storage system as well.
+  if (chosen.height() > ideal_icon_size_in_px) {
+    content::BrowserThread::PostTask(
+        content::BrowserThread::IO,
+        FROM_HERE,
+        base::Bind(&ManifestIconDownloader::ScaleIcon,
+                   ideal_icon_size_in_px,
+                   chosen,
+                   callback));
+    return;
+  }
+
+  callback.Run(chosen);
+}
+
+void ManifestIconDownloader::ScaleIcon(
+    const int ideal_icon_size_in_px,
+    const SkBitmap& bitmap,
+    const ManifestIconDownloader::IconFetchCallback& callback) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+
+  const SkBitmap& scaled = skia::ImageOperations::Resize(
+      bitmap,
+      skia::ImageOperations::RESIZE_BEST,
+      ideal_icon_size_in_px,
+      ideal_icon_size_in_px);
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI,
+      FROM_HERE,
+      base::Bind(callback, scaled));
+}
+
+int ManifestIconDownloader::FindClosestBitmapIndex(
+    int ideal_icon_size_in_px,
+    const std::vector<SkBitmap>& bitmaps) {
+  // There might be multiple bitmaps returned. The one to pick is bigger or
+  // equal to the preferred size. |bitmaps| is ordered from bigger to smaller.

[gone, 2015/08/19 22:21:07]

the explicit restriction on |bitmaps| should be put in header as a function
comment

[Lalit Maganti, 2015/08/20 16:48:00]

Done.

+  int best_index = -1;
+  for (size_t i = 0; i < bitmaps.size(); ++i) {
+    if (bitmaps[i].height() != bitmaps[i].width())
+      continue;
+    if (bitmaps[i].height() == ideal_icon_size_in_px)
+      return i;
+    if (bitmaps[i].height() < ideal_icon_size_in_px)
+      break;
+    best_index = i;
+  }
+  return best_index;
+}