Split initial methods of left/right/top/bottom on ComputedStyle.

Currently the left, right, top and bottom share the same method for
the initial value: initialOffset(). This makes it difficult to generate
because the generator will generate four copies of initialOffset(),
causing a name conflict.

This patch splits the initialOffset() method into four separate methods,
one for each property.

Diff of generated files:
https://gist.github.com/darrnshn/88a94abf4e37e26b7fdcc4126beb11fa/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2815033002
Cr-Commit-Position: refs/heads/master@{#464313}
2 files changed