[Cronet] Implement batch read in CronetInputStream

Also added a test to test that batch read works when
getMoreData() is called multiple times (i.e when the data is
large).
There are existing test cases for batch read (testInputStreamReadMoreBytesThanAvailable,
testInputStreamReadExactBytesAvailable, and
testInputStreamReadLessBytesThanAvailable)

BUG=398997

Review URL: https://codereview.chromium.org/972213002

Cr-Commit-Position: refs/heads/master@{#320815}
3 files changed