Use NSURLSession if the min version we support is iOS 7+.
Use NSURLSession if the min version we support is iOS 7+.

Because many apps still support iOS 8, they were defaulting to
deprecated NSURLConnection even if the code ran on iOS 10.
NSURLConnection requires a run loop and hence the code did not
always upload if the queue ran on a thread without a Run Loop.
This should improve break pad uploads

BUG=

Change-Id: I7bff80ea977fd1ab13c8812ed933ef842dab417f
Reviewed-on: https://chromium-review.googlesource.com/451880
Reviewed-by: Sylvain Defresne <075a4f7f645ca1869f9f673a573a0cfb60d14733@chromium.org>
Reviewed-by: Mark Mentovai <f1b5a91d4d6ad523f2610114591c007e75d15084@chromium.org>

bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad,bittorrent/breakpad