The Concise New Partridge Dictionary of Slang (2007) says:
burroo; brew; buro noun an unemployment exchange; the Department of Social Security. Form a Glasgow pronunciation of 'bureau' as in 'Employment Bureau. UK, 1937
On the brew means being unemployed or receiving unemployment benefits, and is similar to on the dole.
The oldest I found in Google Books for the exact phrase on the brew is in the New York Magazine (Vol. 2, No. 11) of 17 Mar 1969, in an interview with New York immigrant James Toner from Belfast, Northern Ireland:
"What do the Catholics do for work?"
"Go on the brew. You know the stayet. The Relief. Then they hang around the bars and the bookie shops. There's nothin' else they can do."
I've never heard it before, but I've never lived in Scotland. It is still used by people in the Glasgow area. Looking for current usage, I searched Twitter and found this from someone in Glasgow:
some c*ltic fans on this clearly should have been lawyers insted of sittin on the brew shut up and accept 54 titles and still goin strong
And this from someone in Cumnock (39 miles from Glasgow):
Might be my last week of work need a new job so am no back on the brew #badtimes
And finally, this from someone in Wishaw (15 miles from Glasgow):
Its a nightmare knowing that your monthly wage is going to be less than what a person on the brew gets in 2 weeks. This nation is backwards!
The expression "a kick in the ass" (or, more mildly, "a kick in the pants") is sometimes used to refer to jumpstarting an individual, or getting a situation back on the right track, as in:
"Our son needs to get a job!"
"Yes, he needs a good kick in the pants."
It stands to reason, then, that "boot" can be substituted for "kick," since that's the net result, when the one doing the kicking happens to be wearing boots.
He himself felt sorry for the people who were in horrible pain, but some need the good boot in the ass. (J.E. Jackson, Camp Pain: Talking With Chronic Pain Patients, 1999).
If you want, check out this Ngram. You can see that all these phrases are used, but kick in the pants seems to be most common.
Your example usage:
Does Google need a strong engineer to put a boot in the ass to develop the next XXX ...
reads a little awkward, since it's usually an outsider, or one with some authority, doing the kicking, and it's hard to tell whose butt is going to be kicked in that sentence. (Google's?) If the "strong engineer" is in charge of a group of engineers who are developing XXX, then the expression might work, but I'd probably write more like this:
Google needs a strong engineer to put a boot in the ass of the team developing the next XXX ...
Best Answer
"I'm flattered"; in short, it means the same as "I appreciate it" or "It's nice of you to say"
In the context you've provided, "I'm flattered... I guess" it most like means that this person feels both pleased and awkward because, apparently, they don't feel the same about the other person.
It's a very subtle way of rejecting someone ;)