Adds support for hittesting points on surface quads.

This is the first patch towards adding support for browser-process quad hittesting. This will be used for out of process iframes as a way to determine which process should receive input events.

BUG=491334
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1265013003

Cr-Commit-Position: refs/heads/master@{#342362}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 1f3e4ee..cf62411 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -844,6 +844,7 @@
     "surfaces/surface_aggregator_test_helpers.cc",
     "surfaces/surface_aggregator_test_helpers.h",
     "surfaces/surface_aggregator_unittest.cc",
+    "surfaces/surface_hittest_unittest.cc",
     "surfaces/surface_unittest.cc",
     "surfaces/surfaces_pixeltest.cc",