[Parser] Cache and clone initial AstValueFactory string_table_.

src/isolate.h

 // Copyright 2012 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_ISOLATE_H_
 #define V8_ISOLATE_H_
 
 #include <memory>
 #include <queue>
 
@@ skipping 1141 matching lines @@
   v8::ArrayBuffer::Allocator* array_buffer_allocator() const {
     return array_buffer_allocator_;
   }
 
   FutexWaitListNode* futex_wait_list_node() { return &futex_wait_list_node_; }
 
   CancelableTaskManager* cancelable_task_manager() {
     return cancelable_task_manager_;
   }
 
-  AstStringConstants* ast_string_constants() const {
+  const AstStringConstants* ast_string_constants() const {
     return ast_string_constants_;
   }
 
   interpreter::Interpreter* interpreter() const { return interpreter_; }
 
   AccountingAllocator* allocator() { return allocator_; }
 
   CompilerDispatcher* compiler_dispatcher() const {
     return compiler_dispatcher_;
   }
@@ skipping 229 matching lines @@
   HistogramInfo heap_histograms_[LAST_TYPE + 1];
   JSObject::SpillInformation js_spill_information_;
 #endif
 
   Debug* debug_;
   CpuProfiler* cpu_profiler_;
   HeapProfiler* heap_profiler_;
   std::unique_ptr<CodeEventDispatcher> code_event_dispatcher_;
   FunctionEntryHook function_entry_hook_;
 
-  AstStringConstants* ast_string_constants_;
+  const AstStringConstants* ast_string_constants_;
 
   interpreter::Interpreter* interpreter_;
 
   CompilerDispatcher* compiler_dispatcher_;
 
   typedef std::pair<InterruptCallback, void*> InterruptEntry;
   std::queue<InterruptEntry> api_interrupts_queue_;
 
 #define GLOBAL_BACKING_STORE(type, name, initialvalue)                         \
   type name##_;
@@ skipping 287 matching lines @@
 
   EmbeddedVector<char, 128> filename_;
   FILE* file_;
   int scope_depth_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ISOLATE_H_