Fix chrome.downloads.getFileIcon for hi-dpi and clarify docs.

chrome/common/extensions/api/downloads.idl

 // Copyright (c) 2012 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.
 
 // Use the <code>chrome.downloads</code> API to programmatically initiate,
 // monitor, manipulate, and search for downloads.
 [permissions=downloads]
 namespace downloads {
   [inline_doc] dictionary HeaderNameValuePair {
     // Name of the HTTP header.
@@ skipping 362 matching lines @@
     DoubleDelta? totalBytes;
 
     // The change in <code>fileSize</code>, if any.
     DoubleDelta? fileSize;
 
     // The change in <code>exists</code>, if any.
     BooleanDelta? exists;
   };
 
   [inline_doc] dictionary GetFileIconOptions {
-    // The size of the icon.  The returned icon will be square with dimensions
-    // size * size pixels.  The default size for the icon is 32x32 pixels.
+    // The size of the returned icon. The icon will be square with dimensions
+    // size * size pixels. The default and largest size for the icon is 32x32
+    // pixels. The only supported sizes are 16 and 32. It is an error to specify
+    // any other size.
     [legalValues=(16,32)] long? size;
   };
 
   callback DownloadCallback = void(long downloadId);
   callback SearchCallback = void(DownloadItem[] results);
   callback EraseCallback = void(long[] erasedIds);
   callback NullCallback = void();
   callback GetFileIconCallback = void(optional DOMString iconURL);
   callback SuggestFilenameCallback = void(
     optional FilenameSuggestion suggestion);
@@ skipping 142 matching lines @@
     // <code>suggestion</code> object to <code>suggest</code> wins. In order to
     // avoid confusion regarding which extension will win, users should not
     // install extensions that may conflict. If the download is initiated by
     // $ref:download and the target filename is known before the MIME type and
     // tentative filename have been determined, pass <code>filename</code> to
     // $ref:download instead.
     [maxListeners=1] static void onDeterminingFilename(
         DownloadItem downloadItem, SuggestFilenameCallback suggest);
   };
 };