Revert "lazy instantiation of the default isolate" and "build fix for 17049".

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 6a4c72a1d8dc38365a0bb57588b1ff6bc465c8a0..6693b578f5aaaffe5396d9550a3627a4d1853234 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -491,17 +491,14 @@ class Isolate {
 
   static void GlobalTearDown();
 
-  bool IsDefaultIsolate() const { return is_default_isolate_; }
+  bool IsDefaultIsolate() const { return this == default_isolate_; }
 
   static void SetCrashIfDefaultIsolateInitialized();
   // Ensures that process-wide resources and the default isolate have been
   // allocated. It is only necessary to call this method in rare cases, for
   // example if you are using V8 from within the body of a static initializer.
   // Safe to call multiple times.
-  static Isolate* EnsureDefaultIsolate(bool must_be_null = false);
-
-  // Initialize all thread local variables
-  static void InitializeThreadLocalStorage();
+  static void EnsureDefaultIsolate();
 
   // Find the PerThread for this particular (isolate, thread) combination
   // If one does not yet exist, return null.
@@ -1140,12 +1137,8 @@ class Isolate {
   // Given an address occupied by a live code object, return that object.
   Object* FindCodeObject(Address a);
 
-  static Atomic32 GetLivingIsolates() {
-    return Acquire_Load(&living_isolates_);
-  }
-
  private:
-  explicit Isolate(bool is_default_isolate = false);
+  Isolate();
 
   friend struct GlobalState;
   friend struct InitializeGlobalState;
@@ -1210,11 +1203,11 @@ class Isolate {
   static Thread::LocalStorageKey per_isolate_thread_data_key_;
   static Thread::LocalStorageKey isolate_key_;
   static Thread::LocalStorageKey thread_id_key_;
+  static Isolate* default_isolate_;
   static ThreadDataTable* thread_data_table_;
 
   // A global counter for all generated Isolates, might overflow.
   static Atomic32 isolate_counter_;
-  static Atomic32 living_isolates_;
 
   void Deinit();
 
@@ -1326,9 +1319,6 @@ class Isolate {
   // True if this isolate was initialized from a snapshot.
   bool initialized_from_snapshot_;
 
-  // True only for the default isolate.
-  bool is_default_isolate_;
-
   // Time stamp at initialization.
   double time_millis_at_init_;