Constraint space for current child should be adjusted to offset.

As we now have space_for_current_child_ it should be used to search layout opportunities for floats. Also space_for_current_child_'s offset should be adjusted according to the available space.

List of changes:
- Change FindLayoutOpportunityForFragment to use space_for_current_child_.
- Rename CreateConstraintSpaceForChild -> CreateConstraintSpaceForCurrentChild and make it a private class's method.
- Adjust space_for_current_child_'s offset to the available space.
- Change NGBlockLayoutAlgorithmTest::PositionFloatFragments to include a regular block between floats.

BUG=635619

Review-Url: https://codereview.chromium.org/2468113003
Cr-Commit-Position: refs/heads/master@{#429622}
5 files changed