blink_perf.events: Reduce how much we recurse

This test caused blink to recurse to stacks > 4,000 frames deep. This is
caused crashes for Android on ARM64, which has a standard stack limit of
1MB.

Since it appears that this benchmark's depth is somewhat arbitrary (e.g.
the crashes we're seeing when running the benchmarks aren't indicative
of a problem in the real world), turning down the recursion seems
reasonable here.

Bug: 851539
Test: Ran blink_perf.events on ARM64 Android; no crashes observed.
Change-Id: I71290e7d2ddc4786aa1ba09c5030375d2027b39e
Reviewed-on: https://chromium-review.googlesource.com/1111565Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569685}

third_party/blink/perf_tests/events/EventsDispatchingInDeeplyNestedShadowTrees.html

@@ -44,8 +44,8 @@ function rightMostLeaf(root)
 }
 
 var root = document.getElementById('root');
-createComposedTree(document.getElementById('child1'), 50, 20);
-createComposedTree(document.getElementById('child2'), 50, 20);
+createComposedTree(document.getElementById('child1'), 50, 10);
+createComposedTree(document.getElementById('child2'), 50, 10);
 var leaf1 = leftMostLeaf(root);
 var leaf2 = rightMostLeaf(root);