Generate the storage of pseudoBits and styleType in ComputedStyleBase.

In ComputedStyle, pseudoBits and styleType are two data members used for
storing psuedoelement styles. Their interface is difficult to generate
because:
1) They share the same enum, but not all enum values are valid for
   styleType.
2) pseudoBits is a bit set, which we can't generate yet.

This patch uses the 'storage_only' template to move the storage of both
fields to ComputedStyleBase first, and keep the interfaces handwritten.

This is prework for either generating those fields properly or removing
pseudo style information from ComputedStyle entirely.

Diff of generated files: https://gist.github.com/darrnshn/1044b3bd2822c62072ab6f0e22f43104/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2755053002
Cr-Commit-Position: refs/heads/master@{#459290}
5 files changed