constexpr all the blink geometry types

With constexpr you make it slightly easier for the compiler to
optimize code, though the effect will be small.

Also, with constexpr types the compiler becomes better at telling
us when a variable is unused. This removes such variables.

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6b52edc7ef67167bf8b7864c97a5f57b50d85398
Reviewed-on: https://chromium-review.googlesource.com/1131509
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577950}
31 files changed