[turbofan] reduce allocations outside of pipeline

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index b97260111ea45ffb0ea1683b4347183bb90be733..b230090888cbf25df65a1c01cf536678b97f3e61 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -22,10 +22,10 @@ AstGraphBuilder::AstGraphBuilder(Zone* local_zone, CompilationInfo* info,
     : StructuredGraphBuilder(local_zone, jsgraph->graph(), jsgraph->common()),
       info_(info),
       jsgraph_(jsgraph),
-      globals_(0, info->zone()),
+      globals_(0, local_zone),
       breakable_(NULL),
       execution_context_(NULL) {
-  InitializeAstVisitor(info->zone());
+  InitializeAstVisitor(local_zone);
 }