Move cursor property to be generated in ComputedStyleBase.

Move the inherited property 'cursor' and its enum, ECursor,
to be generated in ComputedStyleBase. Also moved getter / setter /
initial value methods to be generated in ComputedStyleBase. Finally
replaced handwritten conversion between CSSValueID and ECursor with
generated code.

Note that this renames m_cursorStyle to m_cursor to match
the name of the getter/setter. This shouldn't affect anything
since the member is private and only used within the generated
class.

The changes in generated code is triggered by adding the 'keyword'
field_template to the cursor property in CSSProperties.json5.

Diff: https://gist.github.com/darrnshn/2a3770b1721a7354110633a5ea6fcec1/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2742253002
Cr-Commit-Position: refs/heads/master@{#458012}
5 files changed