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Denis Koroskin 44b6200392 Round ShadowNode layout coordinates to a pixel boundary

Summary:
When layout happens, left/top/right/bottom coordinates (and thus clip-*, too) are sometimes not at a pixel boundary for 2 reasons:
a) width/height in Flexbox are floats, and can contain any value, not just a whole pixel. E.g. style={{width: 3.1415926}} is perfectly valid
b) floating point arithmetics sometimes leads to values barely outside of pixel boundaries (width 18.0f can become 18.000001f when a sibling/child size changes).

a) is \"breaking\" screenshot tests, which slightly but differ from reference implementation
b) causes extra View updates/redraws for no reason

This patch is rounding DrawCommand bounds to a whole pixel to avoid these 2 issues.

Reviewed By: ahmedre

Differential Revision: D2934401

2016-12-19 13:40:22 -08:00