Moved nonproperty 'unique' to be generated in ComputedStyleBase.

Currently we are generating some CSS property fields in ComputedStyle.
This patch allows the code generator to generate nonproperty fields as
well. Nonproperty fields are member variables in ComputedStyle that
are not actually CSS properties (e.g. m_isLink, m_unique). Property
fields are mostly enums, whereas most nonproperty fields are boolean
flags.

To show that this is working, this patch move the nonproperty field
'unique' to be generated in ComputedStyleBase. Also moved getter /
setter methods to be generated in ComputedStyleBase.

BUG=628043

Review-Url: https://codereview.chromium.org/2667543002
Cr-Commit-Position: refs/heads/master@{#450238}
4 files changed