Style updates for ForwardErrorCorrection and related classes.

This CL mainly updates the FEC code to use more C++11 features and
to be more in line with the style guide. These changes should
have no impact on the functionality provided by the FEC.

Summary of style fixes:
- Use range-based for loops, where applicable.
- Use auto type deduction for iterator type names.
- Use RTC_DCHECK instead of assert.
- Rename FEC to Fec, where applicable.
- Update test_fec.cc to use variable_names rather than variableNames.
- Avoid redefining the PacketList types outside ForwardErrorCorrection.

Another minor change is that storage for the packet masks, as these
are generated, now is provided by a member variable, rather than
being dynamically allocated on every call to GenerateFec.

BUG=webrtc:5654
R=danilchap@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2080553003 .

Cr-Original-Commit-Position: refs/heads/master@{#13403}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: ae4f7674e472f21701c1e65bc2c9b28e421dee8e
10 files changed