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

chrome/browser/download/download_file_icon_extractor.h

Index: chrome/browser/download/download_file_icon_extractor.h
diff --git a/chrome/browser/download/download_file_icon_extractor.h b/chrome/browser/download/download_file_icon_extractor.h
index f7aa7cf5d73562f6b5ec1c051b85cffe83e0ffa4..454790a23c9a5086cd6963944b53196ff7af7255 100644
--- a/chrome/browser/download/download_file_icon_extractor.h
+++ b/chrome/browser/download/download_file_icon_extractor.h
@@ -25,6 +25,7 @@ class DownloadFileIconExtractor {
   // Should return false if the request was invalid.  If the return value is
   // true, then |callback| should be called with the result.
   virtual bool ExtractIconURLForPath(const base::FilePath& path,
+                                     float scale,
                                      IconLoader::IconSize icon_size,
                                      IconURLCallback callback) = 0;
 };