Remove static initializers in SkCodec

Bug: 768878

Switch const declarations to constexpr where appropriate. Speculative
fix for crbug.com/768878.

Change-Id: I7fc356e623ce7a0f2b87e92e9a8ed95d5c423d79
Reviewed-on: https://skia-review.googlesource.com/54101
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Chris Blume <cblume@chromium.org>
11 files changed