[Jobs]: Boost WaitForConcurrencyIncreaseUpdate timeout to 30sec.

To avoid flaky failures with slow running tests.

Bug: 1046343
Change-Id: Iafb6d15c08fb8c97eaa36d802cee5f993eceacd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107602
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751380}

base/task/thread_pool/job_task_source.cc

@@ -336,7 +336,11 @@ size_t JobTaskSource::GetConcurrencyIncreaseVersion() const {
 
 bool JobTaskSource::WaitForConcurrencyIncreaseUpdate(size_t recorded_version) {
   AutoLock auto_lock(version_lock_);
-  constexpr TimeDelta timeout = TimeDelta::FromSeconds(1);
+  // This timeout is meant to catch a JobDelegate which forgets to decrease the 
+  // max-concurrency it returns despite workers returning (hence entering an 
+  // infinite loop of workers being spawned with no work to do). 30 seconds 
+  // catches this error early enough without causing false positives.
+  constexpr TimeDelta timeout = TimeDelta::FromSeconds(30);
   const base::TimeTicks start_time = subtle::TimeTicksNowIgnoringOverride();
   do {
     DCHECK_LE(recorded_version, increase_version_);