Documentation updates and improved gcc compatibility.

Bug: skia:
Change-Id: I03696aaff38060b00c4929b8b38db63ab0e52b2e
Reviewed-on: https://skia-review.googlesource.com/147868
Reviewed-by: Allan MacKinnon <allanmac@google.com>
Commit-Queue: Allan MacKinnon <allanmac@google.com>
Auto-Submit: Allan MacKinnon <allanmac@google.com>
28 files changed