Implement chrome.downloads.erase()

chrome/common/extensions/api/downloads.idl

Index: chrome/common/extensions/api/downloads.idl
diff --git a/chrome/common/extensions/api/downloads.idl b/chrome/common/extensions/api/downloads.idl
index c3e21828a57542761b6cbf7864f79f0447dcb01d..110932c1856a9a69cd531a033259e9d564ef3995 100644
--- a/chrome/common/extensions/api/downloads.idl
+++ b/chrome/common/extensions/api/downloads.idl
@@ -365,9 +365,10 @@ namespace downloads {
     // |downloadId|: The identifier for the downloaded file.
     static void open(long downloadId);
 
-    // Erase matching $ref:DownloadItem from history
-    [nodoc] static void erase(DownloadQuery query,
-                              optional EraseCallback callback);
+    // Erase matching $ref:DownloadItem from history. An $ref.onErased event
+    // will fire for each $ref.DownloadItem that matches <code>query</code>,
+    // then <code>callback</code> will be called.
+    static void erase(DownloadQuery query, optional EraseCallback callback);
 
     // TODO(benjhayden) Comment.
     [nodoc] static void setDestination(long downloadId, DOMString relativePath);