Add a SafepointMutexLocker class so that it is possible to have scopes inside the MutexLocker which…

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 15c25621b41b78e5bb3e8daa1a1c520307c50b8d..f38a4e12c2d0db60c22516785cf966890437c5f0 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -318,6 +318,7 @@ class Isolate : public BaseIsolate {
   void set_spawn_state(IsolateSpawnState* value) { spawn_state_ = value; }
 
   Mutex* mutex() const { return mutex_; }
+  Mutex* symbols_mutex() const { return symbols_mutex_; }
 
   Debugger* debugger() const {
     if (!FLAG_support_debugger) {
@@ -779,6 +780,7 @@ class Isolate : public BaseIsolate {
   Random random_;
   Simulator* simulator_;
   Mutex* mutex_;  // protects stack_limit_, saved_stack_limit_, compiler stats.
+  Mutex* symbols_mutex_;  // Protects concurrent access to teh symbol table.

[srdjan, 2016/02/19 21:38:05]

s/teh/the/

   uword saved_stack_limit_;
   uword deferred_interrupts_mask_;
   uword deferred_interrupts_;