Updated MallocHooks to collect stack traces when memory is allocated.

runtime/vm/os_thread.h

Index: runtime/vm/os_thread.h
diff --git a/runtime/vm/os_thread.h b/runtime/vm/os_thread.h
index 41e77180ed74cf2dd256c4eede7dd3882b2faaab..70eebbfee09fd2723a62a2c429da26ea19fa35c3 100644
--- a/runtime/vm/os_thread.h
+++ b/runtime/vm/os_thread.h
@@ -116,7 +116,7 @@ class OSThread : public BaseThread {
   bool ThreadInterruptsEnabled();
 
   // The currently executing thread, or NULL if not yet initialized.
-  static OSThread* Current() {
+  static OSThread* TryCurrent() {
     BaseThread* thread = GetCurrentTLS();
     OSThread* os_thread = NULL;
     if (thread != NULL) {
@@ -126,7 +126,15 @@ class OSThread : public BaseThread {
         Thread* vm_thread = reinterpret_cast<Thread*>(thread);
         os_thread = GetOSThreadFromThread(vm_thread);
       }
-    } else {
+    }
+    return os_thread;
+  }
+
+  // The currently executing thread. If there is no currently executing thread,
+  // a new OSThread is created and returned.
+  static OSThread* Current() {
+    OSThread* os_thread = TryCurrent();
+    if (os_thread == NULL) {
       os_thread = CreateAndSetUnknownThread();
     }
     return os_thread;