Make SkCodec truly default to sRGB

Remove SkEncodedInfo::ICCProfile::MakeSRGB. Instead of creating
this object whenever there is no encoded color profile, just
treat null as sRGB, like skcms does.

This may help with crbug.com/887372. Regardless it simplifies the
code.

Also fix a bug where SkCodec could have passed a null
skcms_ICCProfile to skcms_ApproximatelyEqualProfiles (related
to b/116608007).

Bug: chromium:887372
Change-Id: I2374e8d8a1aed261f1291b7f6fd6c7ea662f26fd
Reviewed-on: https://skia-review.googlesource.com/157561
Auto-Submit: Leon Scroggins <scroggo@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
10 files changed