NGInlineLayoutAlgorithm should take margins of inline floats into account

1) Moved ComputeMarginsForChild to NGLayoutAlgorithm
2) Changed InlineLayoutAlgorithmTest to call ComputeMarginsForChild
   and pass them to NGFloatingObject

BUG=635619
TEST=NGInlineLayoutAlgorithmTest::PositionFloatsWithMargins

Review-Url: https://codereview.chromium.org/2798203002
Cr-Commit-Position: refs/heads/master@{#462644}
2 files changed