cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index c2f1cf48196580900f793e979f5106405e8e8673..fb4c1f2d5c41341f8aded709f1632ba1149d131e 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -55,6 +55,8 @@ component("cc") {
     "base/scoped_ptr_algorithm.h",
     "base/scoped_ptr_deque.h",
     "base/scoped_ptr_vector.h",
+    "base/simple_enclosed_region.cc",
+    "base/simple_enclosed_region.h",
     "base/swap_promise.h",
     "base/swap_promise_monitor.cc",
     "base/swap_promise_monitor.h",
@@ -646,6 +648,7 @@ test("cc_unittests") {
     "base/region_unittest.cc",
     "base/rolling_time_delta_history_unittest.cc",
     "base/scoped_ptr_vector_unittest.cc",
+    "base/simple_enclosed_region_unittest.cc",
     "base/tiling_data_unittest.cc",
     "base/util_unittest.cc",
     "debug/micro_benchmark_controller_unittest.cc",