Fixed compilation time measurement, restructure some code.

runtime/vm/allocation.h

Index: runtime/vm/allocation.h
===================================================================
--- runtime/vm/allocation.h	(revision 7417)
+++ runtime/vm/allocation.h	(working copy)
@@ -42,20 +42,22 @@
     // We can only have longjumps and exceptions when there is a current
     // isolate.  If there is no current isolate, we don't need to
     // protect this case.
-    if (isolate) {
+    if (isolate != NULL) {
       previous_ = isolate->top_resource();
       isolate->set_top_resource(this);
     }
   }
 
   virtual ~StackResource() {
-    if (isolate()) {
+    if (isolate() != NULL) {
       StackResource* top = isolate()->top_resource();
       ASSERT(top == this);
       isolate()->set_top_resource(previous_);
     }
 #if defined(DEBUG)
-    BaseIsolate::AssertCurrent(isolate());
+    if (isolate() != NULL) {
+      BaseIsolate::AssertCurrent(isolate());
+    }
 #endif
   }