G3: Add support for recursive progressiveEnhancement

The cancel button progressive enhancement moved inside the
topic reply form progressive enhancement requiring support
for recursive progressive enhancement.

Only supports one level of recursion for now.
When we need more levels we'll revisit this.

Change-Id: I593efd6fc9f886684e199b3611b8789e41c71365
Merge "G3: Add support for recursive progressiveEnhancement"