Introduce per-isolate assert scopes and API to guard JS execution.

test/cctest/test-strings.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 643 matching lines @@
 
 template<typename BuildString>
 void TestStringCharacterStream(BuildString build, int test_cases) {
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   HandleScope outer_scope(isolate);
   ConsStringGenerationData data(true);
   for (int i = 0; i < test_cases; i++) {
     printf("%d\n", i);
     HandleScope inner_scope(isolate);
-    AlwaysAllocateScope always_allocate;
+    AlwaysAllocateScope always_allocate(isolate);
     // Build flat version of cons string.
     Handle<String> flat_string = build(i, &data);
     ConsStringStats flat_string_stats;
     AccumulateStats(flat_string, &flat_string_stats);
     // Flatten string.
     FlattenString(flat_string);
     // Build unflattened version of cons string to test.
     Handle<String> cons_string = build(i, &data);
     ConsStringStats cons_string_stats;
     AccumulateStats(cons_string, &cons_string_stats);
@@ skipping 694 matching lines @@
       CheckCanonicalEquivalence(c, test);
       continue;
     }
     if (upper != c && lower != c) {
       CheckCanonicalEquivalence(c, test);
       continue;
     }
     CHECK_EQ(Min(upper, lower), test);
   }
 }