Reland r286968: The CL borrows ShareDialog from Files.app and add it to Gallery.

Previous Review URL: https://codereview.chromium.org/431293002

BUG=374667
TEST=manually
R=yoshiki@chromium.org, mtomasz@chromium.org

Review URL: https://codereview.chromium.org/433733004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286975 0039d316-1c4b-4281-b951-d872f2087c98
    ~FileBrowserPrivateGetDriveFilesFunction() {
}

    ~FileBrowserPrivateGetDriveFilesFunction() {
}
