Clean up naming in ComputedStyle

Clean up some naming in ComputedStyle, as pre-work to adding a fast-path
for inherited properties (which breaks up some of these functions even
further, and relies on accurate naming of members and is confusing if
they both use the term 'flags').

- Rename Non/InheritedFlags to Non/InheritedData (so as not to conflict
  with actual flags landing in the next patch)
- Renamed inheritedNotEqual() methods on ComputedStyle and
  SVGComputedStyle to be inheritedEqual() instead, as this will be less
  confusing later
- Changed operator== on ComputedStyle and SVGComputedStyle to use
  inheritedEqual() and nonInheritedEqual() internally, to reduce code
  repeats of fields
- Renamed a bunch of fields in ComputedStyle to begin with m_ and use
  proper camelcase from style guide
- Changed some ASSERTs to DCHECKs in ComputedStyle

BUG=622138

Review-Url: https://codereview.chromium.org/2115803002
Cr-Commit-Position: refs/heads/master@{#403850}
4 files changed