Migrate most uses of Isolate::current_zone to Thread::zone.

runtime/vm/flow_graph_range_analysis.cc

 // Copyright (c) 2014, 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_range_analysis.h"
 
 #include "vm/bit_vector.h"
 #include "vm/il_printer.h"
 
 namespace dart {
@@ skipping 1498 matching lines @@
       f->Print("v%" Pd "", index_bound->ssa_temp_index());
     }
     f->Print(" {%s}", Range::ToCString(index_bound->range()));
   }
 
 
   static const char* IndexBoundToCString(Definition* index_bound) {
     char buffer[1024];
     BufferFormatter f(buffer, sizeof(buffer));
     PrettyPrintIndexBoundRecursively(&f, index_bound);
-    return Isolate::Current()->current_zone()->MakeCopyOfString(buffer);
+    return Thread::Current()->zone()->MakeCopyOfString(buffer);
   }
 
   RangeAnalysis* range_analysis_;
   FlowGraph* flow_graph_;
   Scheduler scheduler_;
 };
 
 
 void RangeAnalysis::EliminateRedundantBoundsChecks() {
   if (FLAG_array_bounds_check_elimination) {
@@ skipping 1630 matching lines @@
     }
   } while (CanonicalizeMaxBoundary(&max) ||
            CanonicalizeMinBoundary(&canonical_length));
 
   // Failed to prove that maximum is bounded with array length.
   return false;
 }
 
 
 }  // namespace dart