[File Manager] Support HiDPI images in action picker and default action picker

[File Manager] Support HiDPI images in action picker and default action picker

Also fixed a minor bug in the default action picker title.

BUG=
TEST=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=147851

[Vladislav Kaznacheev, 2012-07-20 15:40:13]

Please review

[Dmitry Zvorygin, 2012-07-20 16:13:42]

https://chromiumcodereview.appspot.com/10790100/diff/3001/chrome/browser/reso...
File chrome/browser/resources/file_manager/js/file_manager.js (right):

https://chromiumcodereview.appspot.com/10790100/diff/3001/chrome/browser/reso...
chrome/browser/resources/file_manager/js/file_manager.js:2541: if
(extensions.length == 1) {
It's my fault here, but if extensions.length > 1, we should set format to
something like "extensions.join(', ')".

https://chromiumcodereview.appspot.com/10790100/diff/17/chrome/browser/resour...
File chrome/browser/resources/file_manager/js/mock_chrome.js (right):

https://chromiumcodereview.appspot.com/10790100/diff/17/chrome/browser/resour...
chrome/browser/resources/file_manager/js/mock_chrome.js:155: iconType: 'generic'
You don't use task.iconType in code currently, and task.iconUrl doesn't work at
all according to comment 
" file_browser.js:68
// TODO(serya): This hack needed until task.iconUrl is working
//             (see GetFileTasksFileBrowserFunction::RunImpl).
"

What was this change made for?

[Dmitry Zvorygin, 2012-07-20 16:15:39]

LGTM with comments addressed.

[commit-bot: I haz the power, 2012-07-20 16:18:54]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.