1. Avoid potential dead lock due to lock-order-inversion

runtime/vm/precompiler.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/precompiler.h"
 
 #include "vm/aot_optimizer.h"
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/branch_optimizer.h"
@@ skipping 1983 matching lines @@
   Array& constants = Array::Handle(Z);
   String& name = String::Handle(Z);
 
 #if defined(DEBUG)
   // We are about to remove classes from the class table. For this to be safe,
   // there must be no instances of these classes on the heap, not even
   // corpses because the class table entry may be used to find the size of
   // corpses. Request a full GC and wait for the sweeper tasks to finish before
   // we continue.
   I->heap()->CollectAllGarbage();
-  I->heap()->WaitForSweeperTasks();
+  I->heap()->WaitForSweeperTasks(T);
 #endif
 
   ClassTable* class_table = I->class_table();
   intptr_t num_cids = class_table->NumCids();
 
   for (intptr_t cid = kNumPredefinedCids; cid < num_cids; cid++) {
     if (!class_table->IsValidIndex(cid)) continue;
     if (!class_table->HasValidClassAt(cid)) continue;
 
     cls = class_table->At(cid);
@@ skipping 1640 matching lines @@
 
   ASSERT(FLAG_precompiled_mode);
   const bool optimized = function.IsOptimizable();  // False for natives.
   DartPrecompilationPipeline pipeline(zone, field_type_map);
   return PrecompileFunctionHelper(precompiler, &pipeline, function, optimized);
 }
 
 #endif  // DART_PRECOMPILER
 
 }  // namespace dart