[Android]: Fix hang in CreateChildCrash() on Android.
[Android]: Fix hang in CreateChildCrash() on Android.

After r1299, the LinuxCoreDumperTest::VerifyDumpWithMultipleThreads and
ElfCoreDumpTest::ValidCoreFile would both hang on Android.  This appears to be due to the tkill
signal not being recieved by the thread which is meant to crash, even though tkill returns 0.
This CL retries sending the tkill signal multiple times, which prevents the Hang.

BUG=579
R=thestig@chromium.org

Review URL: https://breakpad.appspot.com/1524002

git-svn-id: 7939527bf0a06ad24ad020f729d5600cb42ed5d7@1313 4c0a9323-5329-0410-9bdc-e9ce6186880e

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