Introduce simple Thread class to support gradual refactoring of interfaces.

runtime/vm/flow_graph_allocator.cc

 // Copyright (c) 2013, 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/flow_graph_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/intermediate_language.h"
 #include "vm/il_printer.h"
 #include "vm/flow_graph.h"
@@ skipping 146 matching lines @@
     BlockEntryInstr* block = postorder_[i];
 
     BitVector* kill = kill_[i];
     BitVector* live_in = live_in_[i];
 
     // Iterate backwards starting at the last instruction.
     for (BackwardInstructionIterator it(block); !it.Done(); it.Advance()) {
       Instruction* current = it.Current();
 
       // Initialize location summary for instruction.
-      current->InitializeLocationSummary(isolate()->current_zone(),
-                                         true);  // opt
+      current->InitializeLocationSummary(zone(), true);  // opt
       LocationSummary* locs = current->locs();
 #if DEBUG
       locs->DiscoverWritableInputs();
 #endif
 
       // Handle definitions.
       Definition* current_def = current->AsDefinition();
       if ((current_def != NULL) && current_def->HasSSATemp()) {
         kill->Add(current_def->ssa_temp_index());
         live_in->Remove(current_def->ssa_temp_index());
@@ skipping 2794 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart