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

src/heap-profiler.cc

 // Copyright 2009-2010 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 159 matching lines @@
   heap()->EnableInlineAllocation();
   is_tracking_allocations_ = false;
   DropCompiledCode();
 }
 
 
 void HeapProfiler::DropCompiledCode() {
   Isolate* isolate = heap()->isolate();
   HandleScope scope(isolate);
 
-  if (FLAG_concurrent_recompilation) {
+  if (isolate->concurrent_recompilation_enabled()) {
     isolate->optimizing_compiler_thread()->Flush();
   }
 
   Deoptimizer::DeoptimizeAll(isolate);
 
   Handle<Code> lazy_compile =
       Handle<Code>(isolate->builtins()->builtin(Builtins::kLazyCompile));
 
   heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask,
                             "switch allocations tracking");
@@ skipping 14 matching lines @@
       if (kind == Code::FUNCTION || kind == Code::BUILTIN) {
         function->set_code(*lazy_compile);
         shared->set_code(*lazy_compile);
       }
     }
   }
 }
 
 
 } }  // namespace v8::internal