Remove the dependency of Zone on Isolate

test/unittests/compiler/loop-peeling-unittest.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/access-builder.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/graph-visualizer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/loop-peeling.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 46 matching lines @@
  protected:
   MachineOperatorBuilder machine_;
 
   MachineOperatorBuilder* machine() { return &machine_; }
 
   LoopTree* GetLoopTree() {
     if (FLAG_trace_turbo_graph) {
       OFStream os(stdout);
       os << AsRPO(*graph());
     }
-    Zone zone(isolate());
+    Zone zone;
     return LoopFinder::BuildLoopTree(graph(), &zone);
   }
 
 
   PeeledIteration* PeelOne() {
     LoopTree* loop_tree = GetLoopTree();
     return Peel(loop_tree, loop_tree->outer_loops()[0]);
   }
 
   PeeledIteration* Peel(LoopTree* loop_tree, LoopTree::Loop* loop) {
@@ skipping 364 matching lines @@
   EXPECT_THAT(
       r, IsReturn(IsPhi(kMachAnyTagged, phi, IsInt32Constant(0),
                         AllOf(CaptureEq(&merge), IsMerge(b1.if_false, b1f))),
                   start(), CaptureEq(&merge)));
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8