Added tombstones in instrumentation tests results.

If an instrumentation test crashes, tombstones were not captured.
In this cl, tombstones are captured and becomes part of the result.

This is a reland of a previous cl, http://crrev.com/2201833002#ps200001.
The reason for reverting the previous cl is that:
it breaks the stack_tool_for_tombstones step for many bots in
https://build.chromium.org/p/chromium.android.
In this reland, the edge case where there is no tombstone is fixed.

BUG=631213

Committed: https://crrev.com/d7dd97f2828447fb9af45ea119e703500b167cb8
Cr-Commit-Position: refs/heads/master@{#410929}

patch from issue 2201833002 at patchset 200001 (http://crrev.com/2201833002#ps200001)

Review-Url: https://codereview.chromium.org/2237553003
Cr-Commit-Position: refs/heads/master@{#412089}
diff --git a/build/android/test_runner.pydeps b/build/android/test_runner.pydeps
index a751412..574e53c 100644
--- a/build/android/test_runner.pydeps
+++ b/build/android/test_runner.pydeps
@@ -144,3 +144,4 @@
 pylib/utils/test_environment.py
 pylib/valgrind_tools.py
 test_runner.py
+tombstones.py