Shift-Enter should add newline in preformatted

Modified handleEnter to check for the condition that shift-enter
is being pressed inside of a preformatted block. If so, a break
node is inserted.

Bug: 45355
Change-Id: Iae7b3c88b7cd976e519c09821a064078228acc79
Merge "Shift-Enter should add newline in preformatted"