Add asserts to ensure that we:

include/v8.h

Index: include/v8.h
===================================================================
--- include/v8.h	(revision 9277)
+++ include/v8.h	(working copy)
@@ -3498,9 +3498,9 @@
  *
  * v8::Locker is a scoped lock object. While it's
  * active (i.e. between its construction and destruction) the current thread is
- * allowed to use the locked isolate. V8 guarantees that an isolate can be locked
- * by at most one thread at any time. In other words, the scope of a v8::Locker is
- * a critical section.
+ * allowed to use the locked isolate. V8 guarantees that an isolate can be
+ * locked by at most one thread at any time. In other words, the scope of a
+ * v8::Locker is a critical section.
  *
  * Sample usage:
 * \code
@@ -3602,8 +3602,8 @@
   static void StopPreemption();
 
   /**
-   * Returns whether or not the locker for a given isolate, or default isolate if NULL is given,
-   * is locked by the current thread.
+   * Returns whether or not the locker for a given isolate, or default isolate
+   * if NULL is given, is locked by the current thread.
    */
   static bool IsLocked(Isolate* isolate = NULL);