Bug 1313488 - Part 1: Convert XPCOM test TestDeadlockDetector to a gt…

…est. r=froydnj

This converts TestDeadlockDetector to a gtest. The logic for spawning off
subprocesses is replaced with gtest's built-in death tests. On linux this will
clone() the process and assert that the child process generates the appropriate
assertion message. On OSX it will use fork(). In theory this should work on
Windows as well buy spawning a new process but this test currently disabled
there.

MozReview-Commit-ID: 9Sl0hHBVGT3

testing/cppunittest.ini

@@ -15,8 +15,6 @@ skip-if = os != 'win'
 [TestCookie]
 [TestCountPopulation]
 [TestCountZeroes]
-[TestDeadlockDetector]
-skip-if = os == 'b2g' || (os == 'android' && debug) # Bug 1054249
 [TestDeadlockDetectorScalability]
 [TestDllInterceptor]
 skip-if = os != 'win'