[Parser] Introduce AstStringConstants to share constants across AstValueFactory

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 0c0af8472a75f3067d63c17f662b2639d78edd85..a77a871fedfc8af766cdf3c1a11bb4fe2b3ef1b2 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -9,6 +9,7 @@
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
 
+#include "src/ast/ast-value-factory.h"
 #include "src/ast/context-slot-cache.h"
 #include "src/base/hashmap.h"
 #include "src/base/platform/platform.h"
@@ -2375,6 +2376,9 @@ void Isolate::Deinit() {
   delete interpreter_;
   interpreter_ = NULL;
 
+  delete ast_string_constants_;
+  ast_string_constants_ = nullptr;
+
   delete cpu_profiler_;
   cpu_profiler_ = NULL;
 
@@ -2698,6 +2702,11 @@ bool Isolate::Init(Deserializer* des) {
 
   time_millis_at_init_ = heap_.MonotonicallyIncreasingTimeInMs();
 
+  {
+    HandleScope scope(this);
+    ast_string_constants_ = new AstStringConstants(this, heap()->HashSeed());
+  }
+
   if (!create_heap_objects) {
     // Now that the heap is consistent, it's OK to generate the code for the
     // deopt entry table that might have been referred to by optimized code in