Make SkStream readers report failure.

This also fixes an issue noticed while making this change where
SkFontDescriptor improperly round trips negative axis values.

Change-Id: Iacc5929a185659dcacc18c802c4908e4f34c6899
Reviewed-on: https://skia-review.googlesource.com/128341
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
10 files changed