A little bit more of the threads implementation.

The most important change here is understanding that Thread's id_ field
was unrelated to java.lang.Thread's id field.

Change-Id: I832b92145332e1ded63a7824033dae684eeacf28
diff --git a/src/runtime.h b/src/runtime.h
index 8a6ffe3..db86a96 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -68,6 +68,8 @@
   // Starts a runtime, which may cause threads to be started and code to run.
   void Start();
 
+  bool IsStarted();
+
   static Runtime* Current() {
     return instance_;
   }
@@ -119,8 +121,7 @@
  private:
   static void PlatformAbort(const char*, int);
 
-  Runtime() : stack_size_(0), thread_list_(NULL), intern_table_(NULL), class_linker_(NULL),
-    signal_catcher_(NULL) {}
+  Runtime();
 
   void BlockSignals();
 
@@ -141,6 +142,8 @@
 
   JavaVMExt* java_vm_;
 
+  bool started_;
+
   // Hooks supported by JNI_CreateJavaVM
   jint (*vfprintf_)(FILE* stream, const char* format, va_list ap);
   void (*exit_)(jint status);