Rename LayoutTable::CollapseBorders() to ShouldCollapseBorders()

The method returns true if the table has "border-collapse: collapse"
style. A better name could be CollapsesBorders() to reflect its
purpose, but both this name and the original name are easily confusing
with another method "CollapsedBorders()".
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2850633003
Cr-Commit-Position: refs/heads/master@{#468443}
9 files changed