Comment context lines are returned from the comments API if the
parameter "enable-context" is set. Each CommentInfo will include an
additional contextLines field, which is a list of {line_number,
line_text}, which are some lines of the source file where the comment
was written.
In this change, the context lines are exactly the lines highlighted by
the user when the comment was written. In a later change, the
"enable-context" parameter will be changed to an integer parameter. The
caller will decide how many lines to retrieve.
Change-Id: I76928de54818fa63b5b49b8e89244c5289361af4
5c4fffb18e