Implement chrome.downloads.onDeterminingFilename() to allow extensions to participate in the download filename determination process.

Docs staged: http://basho.cam.corp.google.com:8000/extensions/downloads.html#event-onDeterminingFilename

Example:
chrome.downloads.onDeterminingFilename.addListener(function(item, suggest) {
  suggest({filename: item.filename, overwrite: true});
});
chrome.downloads.onDeterminingFilename.addListener(function(item, suggest) {
  window.setTimeout(function() {
    suggest({filename: item.mime.split('/')[0] + '/' + item.filename, overwrite: false});
  }, 1);
  return true;  // handling asynchronously
});

BUG=12133
BUG=68108

Review URL: https://chromiumcodereview.appspot.com/11574006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185811 0039d316-1c4b-4281-b951-d872f2087c98
33 files changed