Make number of available threads isolate-dependent and expose it to ResourceConstraints.

test/cctest/test-heap.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 2945 matching lines @@
   const char* data_;
   size_t length_;
 };
 
 
 void ReleaseStackTraceDataTest(const char* source, const char* accessor) {
   // Test that the data retained by the Error.stack accessor is released
   // after the first time the accessor is fired.  We use external string
   // to check whether the data is being released since the external string
   // resource's callback is fired when the external string is GC'ed.
-  FLAG_use_ic = false;  // ICs retain objects.
-  FLAG_concurrent_recompilation = false;
   v8::HandleScope scope(CcTest::isolate());
   SourceResource* resource = new SourceResource(i::StrDup(source));
   {
     v8::HandleScope scope(CcTest::isolate());
     v8::Handle<v8::String> source_string = v8::String::NewExternal(resource);
     CcTest::heap()->CollectAllAvailableGarbage();
     v8::Script::Compile(source_string)->Run();
     CHECK(!resource->IsDisposed());
   }
   // CcTest::heap()->CollectAllAvailableGarbage();
   CHECK(!resource->IsDisposed());
 
   CompileRun(accessor);
   CcTest::heap()->CollectAllAvailableGarbage();
 
   // External source has been released.
   CHECK(resource->IsDisposed());
   delete resource;
 }
 
 
 TEST(ReleaseStackTraceData) {
+  FLAG_use_ic = false;  // ICs retain objects.
+  FLAG_concurrent_recompilation = false;
   CcTest::InitializeVM();
   static const char* source1 = "var error = null;            "
   /* Normal Error */           "try {                        "
                                "  throw new Error();         "
                                "} catch (e) {                "
                                "  error = e;                 "
                                "}                            ";
   static const char* source2 = "var error = null;            "
   /* Stack overflow */         "try {                        "
                                "  (function f() { f(); })(); "
@@ skipping 542 matching lines @@
   CompileRun("run()");
 
   // Run test with inline allocation disabled and pretenuring.
   CcTest::heap()->SetNewSpaceHighPromotionModeActive(true);
   CompileRun("run()");
 
   // Run test with inline allocation re-enabled.
   CcTest::heap()->EnableInlineAllocation();
   CompileRun("run()");
 }