crash-reporter: Replace scoped_ptr<char[]> with vector<char>.

BUG=None
TEST=`FEATURES=test emerge-$BOARD platform2`

Change-Id: I78d7766b49151f40f42ef00b8204fd2569b45991
Reviewed-on: https://chromium-review.googlesource.com/214780


Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>