Some thread data simplifications.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 741c4c02ffb17cf409f16a4067e3fd560bc5e2b2..f0854e510e510c445c3a1f610ad82539d388e769 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1155,7 +1155,6 @@ class Isolate {
 
     PerIsolateThreadData* Lookup(Isolate* isolate, ThreadId thread_id);
     void Insert(PerIsolateThreadData* data);
-    void Remove(Isolate* isolate, ThreadId thread_id);
     void Remove(PerIsolateThreadData* data);
     void RemoveAllThreads(Isolate* isolate);
 
@@ -1190,7 +1189,7 @@ class Isolate {
 
   // This mutex protects highest_thread_id_, thread_data_table_ and
   // default_isolate_.
-  static RecursiveMutex process_wide_mutex_;
+  static Mutex process_wide_mutex_;
 
   static Thread::LocalStorageKey per_isolate_thread_data_key_;
   static Thread::LocalStorageKey isolate_key_;
@@ -1206,10 +1205,6 @@ class Isolate {
   static void SetIsolateThreadLocals(Isolate* isolate,
                                      PerIsolateThreadData* data);
 
-  // Allocate and insert PerIsolateThreadData into the ThreadDataTable
-  // (regardless of whether such data already exists).
-  PerIsolateThreadData* AllocatePerIsolateThreadData(ThreadId thread_id);
-
   // Find the PerThread for this particular (isolate, thread) combination.
   // If one does not yet exist, allocate a new one.
   PerIsolateThreadData* FindOrAllocatePerThreadDataForThisThread();