Automatically generate EBreakBetween & EBreakInside

The change updates CSSProperties.json5 to cause the EBreakBetween &
EBreakInside enums to be automatically generated in
ComputedStyleBase.cpp.

The manual definition of these enums and any relevant getters, setters,
initializers, and comparitors in ComputedStyle.h/cpp are removed.

BUG=628043

Review-Url: https://codereview.chromium.org/2681833004
Cr-Commit-Position: refs/heads/master@{#450124}
4 files changed