Fix CSS transplantation in IE

Apparently using importNode() to copy a <style> node from
the main document into an iframe doesn't work in IE: the
<style> node is copied over, but its CSS isn't applied or
even parsed.

Work around this by copying over the <style> node's .textContent
manually.

Change-Id: If2c848e9fb53b06a23c85c30a1b56c20854bea50
Merge "Fix CSS transplantation in IE"