Add a TaskPriority cap to the SWP redirection to experiment with no redirections at USER_BLOCKING.

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
diff --git a/base/threading/sequenced_worker_pool.cc b/base/threading/sequenced_worker_pool.cc
index b7e93bb72ab92dbade351dbfd73768ce77c5e0da..56bbb62dd09f58bb92f05340598a109e715c5aee 100644
--- a/base/threading/sequenced_worker_pool.cc
+++ b/base/threading/sequenced_worker_pool.cc
@@ -75,6 +75,8 @@ enum class AllPoolsState {
 // debug::DumpWithoutCrashing() in case of waterfall failures.
 AllPoolsState g_all_pools_state = AllPoolsState::USE_WORKER_POOL;
 
+TaskPriority g_max_task_priority = TaskPriority::HIGHEST;
+
 struct SequencedTask : public TrackingInfo  {
   SequencedTask()
       : sequence_token_id(0),
@@ -644,7 +646,10 @@ SequencedWorkerPool::Inner::Inner(SequencedWorkerPool* worker_pool,
       cleanup_idlers_(0),
       cleanup_cv_(&lock_),
       testing_observer_(observer),
-      task_priority_(task_priority) {
+      task_priority_(static_cast<int>(task_priority) <=
+                             static_cast<int>(g_max_task_priority)

[dcheng, 2016/12/15 21:20:49]

Yay, C++.

+                         ? task_priority
+                         : g_max_task_priority) {
   DCHECK_GT(max_threads_, 1U);
 }
 
@@ -1422,13 +1427,15 @@ void SequencedWorkerPool::EnableForProcess() {
 }
 
 // static
-void SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess() {
+void SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess(
+    TaskPriority max_task_priority) {
   // TODO(fdoray): Uncomment this line. It is initially commented to avoid a
   // revert of the CL that adds debug::DumpWithoutCrashing() in case of
   // waterfall failures.
   // DCHECK_EQ(AllPoolsState::POST_TASK_DISABLED, g_all_pools_state);
   DCHECK(TaskScheduler::GetInstance());
   g_all_pools_state = AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER;
+  g_max_task_priority = max_task_priority;
 }
 
 // static