Allow the user to begin editing the commit message, dismiss the
box by clicking outside of it (e.g. to copy part of a file name
from the Files table), and then re-open the current draft text
without resetting the box.
Only reset the box when the user explicitly clicks Cancel. Track
this by using the empty string in the text editor to mean there
is no valid message and the current original should be used.
Change-Id: Icd99b92c50ff92e0b1dc31a78fc57612f57a143b
0e26575790