Fix libchromeos unittests

A CL (https://android-review.googlesource.com/#/c/169912) added extra
call to get the status code of request for logging which broke
HttpCurlTransportAsyncTest.StartAsyncTransfer due to an unexpected
method call of a mock.

Also, FileStreamTest.FromFileDescriptor_WriteNonBlocking took over
4 seconds on dragonboard and there is no real reason to create
a 10 MB buffer to test pipes which use only 64K. Reducing the buffer
size brought the test execution time to 136 ms.

BUG: 23942116
Change-Id: Ib0bc5ac6ffc7bd96ef3946c31d0cda283756bd82
2 files changed