Add Dart_Null, Dart_True, and Dart_False.

runtime/vm/dart_api_state.h

Index: runtime/vm/dart_api_state.h
===================================================================
--- runtime/vm/dart_api_state.h	(revision 1035)
+++ runtime/vm/dart_api_state.h	(working copy)
@@ -257,17 +257,25 @@
 // basis and destroyed when the isolate is shutdown.
 class ApiState {
  public:
-  ApiState() : top_scope_(NULL), true_(NULL) { }
+  ApiState() : top_scope_(NULL), null_(NULL), true_(NULL), false_(NULL) { }
   ~ApiState() {
     while (top_scope_ != NULL) {
       ApiLocalScope* scope = top_scope_;
       top_scope_ = top_scope_->previous();
       delete scope;
     }
+    if (null_ != NULL) {
+      persistent_handles().FreeHandle(null_);
+      null_ = NULL;
+    }
     if (true_ != NULL) {
       persistent_handles().FreeHandle(true_);
       true_ = NULL;
     }
+    if (false_ != NULL) {
+      persistent_handles().FreeHandle(false_);
+      false_ = NULL;
+    }
   }
 
   // Accessors.
@@ -327,6 +335,17 @@
     }
     return total;
   }
+  PersistentHandle* Null() {
+    if (null_ == NULL) {
+      Zone zone;  // Setup a VM zone as we are creating some handles.
+      HandleScope scope;  // Setup a VM handle scope.
+
+      Object& null_object = Object::Handle();
+      null_ = persistent_handles().AllocateHandle();
+      null_->set_raw(null_object);
+    }
+    return null_;
+  }
   PersistentHandle* True() {
     if (true_ == NULL) {
       Zone zone;  // Setup a VM zone as we are creating some handles.
@@ -338,13 +357,26 @@
     }
     return true_;
   }
+  PersistentHandle* False() {
+    if (false_ == NULL) {
+      Zone zone;  // Setup a VM zone as we are creating some handles.
+      HandleScope scope;  // Setup a VM handle scope.
 
+      const Object& false_object = Object::Handle(Bool::False());
+      false_ = persistent_handles().AllocateHandle();
+      false_->set_raw(false_object);
+    }
+    return false_;
+  }
+
  private:
   PersistentHandles persistent_handles_;
   ApiLocalScope* top_scope_;
 
-  // A persistent handle to the "True" object.
+  // Persistent handles to important objects.
+  PersistentHandle* null_;
   PersistentHandle* true_;
+  PersistentHandle* false_;
 
   DISALLOW_COPY_AND_ASSIGN(ApiState);
 };