Implement platform_util::OpenExternal on ChromeOS

And remove OS-conditional code from ChromeShellWindowDelegate.

BUG=249265,256338

Review URL: https://chromiumcodereview.appspot.com/18083022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@209751 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed