[scheduler] Do not use kInternalIPC in modules/background_sync

Remove kInternalIPC task type.
- If it's used to bind associated interface, use
  kInternalNavigationAssociated instead.
- If it's used to bind non-associated interface, use the task source
  mentioned in the spec, kMiscPlatformAPI if it's not speced yet or
  kInternalDefault if it's a non-spec-related task.

R=falken@chromium.org

Change-Id: Ib693ffc41d9c096f3ed6d4e4ab9797cf8fdd1773
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888031Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711679}

third_party/blink/renderer/modules/background_sync/service_worker_registration_sync.cc

@@ -40,9 +40,10 @@ SyncManager* ServiceWorkerRegistrationSync::sync(
 SyncManager* ServiceWorkerRegistrationSync::sync() {
   if (!sync_manager_) {
     ExecutionContext* execution_context = registration_->GetExecutionContext();
+    // TODO(falken): Consider defining a task source in the spec for this event.
     sync_manager_ = SyncManager::Create(
         registration_,
-        execution_context->GetTaskRunner(TaskType::kInternalIPC));
+        execution_context->GetTaskRunner(TaskType::kMiscPlatformAPI));
   }
   return sync_manager_.Get();
 }
@@ -55,9 +56,10 @@ PeriodicSyncManager* ServiceWorkerRegistrationSync::periodicSync(
 PeriodicSyncManager* ServiceWorkerRegistrationSync::periodicSync() {
   if (!periodic_sync_manager_) {
     ExecutionContext* execution_context = registration_->GetExecutionContext();
+    // TODO(falken): Consider defining a task source in the spec for this event.
     periodic_sync_manager_ = PeriodicSyncManager::Create(
         registration_,
-        execution_context->GetTaskRunner(TaskType::kInternalIPC));
+        execution_context->GetTaskRunner(TaskType::kMiscPlatformAPI));
   }
   return periodic_sync_manager_.Get();
 }