Update supported javascript mimetypes

This patch adds support for the following javascript
mimetypes:
text/javascript1.0
text/javascript1.4
text/javascript1.5
text/x-javascript
text/x-ecmascript
application/x-ecmascript

Which we are required to support per the spec at
https://html.spec.whatwg.org/#javascript-mime-type

BUG=582662

Review-Url: https://codereview.chromium.org/2135753002
Cr-Commit-Position: refs/heads/master@{#404681}
8 files changed