Inline LayoutRect::enclosingIntRect

Noticed this function was hot on blink_perf.paint's color-changes.html
microbenchmark. With this patch, color-changes.html runs 2.7% faster
(average -0.8ms) but that number should be taken with a grain of salt
since it's near the standard deviation of the test.

Manual profiling with and without the patch confirmed this function is
no longer hot.

Review-Url: https://codereview.chromium.org/2550083002
Cr-Commit-Position: refs/heads/master@{#436323}
2 files changed