[Sync] Add an error integration test for USS.

components/sync/driver/data_type_manager_impl.cc

Index: components/sync/driver/data_type_manager_impl.cc
diff --git a/components/sync/driver/data_type_manager_impl.cc b/components/sync/driver/data_type_manager_impl.cc
index 0f6b78bd3c80806171ee4bf3cea709cc98d0f4e1..4d9f1f00bfd913ffe19ce69739abedd593dd2904 100644
--- a/components/sync/driver/data_type_manager_impl.cc
+++ b/components/sync/driver/data_type_manager_impl.cc
@@ -15,6 +15,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/stringprintf.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
 #include "components/sync/core/data_type_debug_info_listener.h"
 #include "components/sync/driver/data_type_encryption_handler.h"
@@ -332,7 +333,10 @@ TypeSetPriorityList DataTypeManagerImpl::PrioritizeTypes(
 }
 
 void DataTypeManagerImpl::ProcessReconfigure() {
-  DCHECK(needs_reconfigure_);
+  // This may have been called asynchronously; no-op if it is no longer needed.
+  if (!needs_reconfigure_) {
+    return;
+  }
 
   // Wait for current download and association to finish.
   if (!download_types_queue_.empty() ||
@@ -499,7 +503,12 @@ void DataTypeManagerImpl::OnSingleDataTypeWillStop(
     if (error.error_type() != syncer::SyncError::UNRECOVERABLE_ERROR) {
       needs_reconfigure_ = true;
       last_configure_reason_ = syncer::CONFIGURE_REASON_PROGRAMMATIC;
-      ProcessReconfigure();
+      // Do this asynchronously so the ModelAssociationManager has a chance to
+      // finish stopping this type, otherwise DeactivateDataType() and Stop()
+      // end up getting called twice on the controller.
+      base::ThreadTaskRunnerHandle::Get()->PostTask(

[skym, 2016/09/27 20:24:45]

Is this really the best way to fix this? I worry that sprinkling PostTasks all
over the code base is going to make things messy long term.

ProcessReconfigure() already has an abort check if 

model_association_manager_.state() ==
          ModelAssociationManager::ASSOCIATING

Maybe we could continue to do something like this. I'm not sure.

[maxbogue, 2016/09/28 20:17:09]

Moving forward with this as discussed offline; Pavel will be refactoring this
code in the near future.

+          FROM_HERE, base::Bind(&DataTypeManagerImpl::ProcessReconfigure,
+                                weak_ptr_factory_.GetWeakPtr()));
     }
   }
 }