cc: Add rtree perftests.

This patch adds some perftests to measure RTree performance.
Sample run (on z620):

[==========] Running 2 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 2 tests from RTreePerfTest
[ RUN      ] RTreePerfTest.Construct
*RESULT rtree_construct: 100= 346091.53125 runs/s
*RESULT rtree_construct: 1000= 36854.61328125 runs/s
*RESULT rtree_construct: 10000= 3392.330322265625 runs/s
*RESULT rtree_construct: 100000= 369.79052734375 runs/s
[       OK ] RTreePerfTest.Construct (8040 ms)
[ RUN      ] RTreePerfTest.Search
*RESULT rtree_search: 100= 2992395.5 runs/s
*RESULT rtree_search: 1000= 507624.9375 runs/s
*RESULT rtree_search: 10000= 32956.60546875 runs/s
*RESULT rtree_search: 100000= 3477.254638671875 runs/s
[       OK ] RTreePerfTest.Search (8020 ms)
[----------] 2 tests from RTreePerfTest (16060 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 1 test case ran. (16060 ms total)
[  PASSED  ] 2 tests.

R=danakj@chromium.org, dskiba@chromium.org
BUG=674169
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2576793002
Cr-Commit-Position: refs/heads/master@{#438675}

• cc/BUILD.gn[diff]
• cc/base/DEPS[diff]
• cc/base/rtree_perftest.cc[Added - diff]