Remove the dependency of Zone on Isolate

src/compiler/js-generic-lowering.h

 // Copyright 2014 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.
 
 #ifndef V8_COMPILER_JS_GENERIC_LOWERING_H_
 #define V8_COMPILER_JS_GENERIC_LOWERING_H_
 
 #include "src/allocation.h"
 #include "src/code-factory.h"
 #include "src/compiler/graph.h"
@@ skipping 33 matching lines @@
   // Helpers to replace existing nodes with a generic call.
   void ReplaceWithCompareIC(Node* node, Token::Value token);
   void ReplaceWithStubCall(Node* node, Callable c, CallDescriptor::Flags flags);
   void ReplaceWithBuiltinCall(Node* node, Builtins::JavaScript id, int args);
   void ReplaceWithRuntimeCall(Node* node, Runtime::FunctionId f, int args = -1);
 
   // Helper for optimization of JSCallFunction.
   bool TryLowerDirectJSCall(Node* node);
 
   Zone* zone() const { return graph()->zone(); }
-  Isolate* isolate() const { return zone()->isolate(); }
+  Isolate* isolate() const { return info_->isolate(); }
   JSGraph* jsgraph() const { return jsgraph_; }
   Graph* graph() const { return jsgraph()->graph(); }
   Linkage* linkage() const { return linkage_; }
   CompilationInfo* info() const { return info_; }
   CommonOperatorBuilder* common() const { return jsgraph()->common(); }
   MachineOperatorBuilder* machine() const { return jsgraph()->machine(); }
 
  private:
   CompilationInfo* info_;
   JSGraph* jsgraph_;
   Linkage* linkage_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_GENERIC_LOWERING_H_