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

src/runtime-profiler.cc

Index: src/runtime-profiler.cc
diff --git a/src/runtime-profiler.cc b/src/runtime-profiler.cc
index 7c900b37d90a6aa87c9ce2f2cb3c124f2268bd7b..691fc6664196b9072d47c1c8eecb66fd6edc6ce7 100644
--- a/src/runtime-profiler.cc
+++ b/src/runtime-profiler.cc
@@ -139,8 +139,9 @@ void RuntimeProfiler::Optimize(JSFunction* function, const char* reason) {
   }
 
 
-  if (FLAG_concurrent_recompilation && !isolate_->bootstrapper()->IsActive()) {
-    if (FLAG_concurrent_osr &&
+  if (isolate_->concurrent_recompilation_enabled() &&
+      !isolate_->bootstrapper()->IsActive()) {
+    if (isolate_->concurrent_osr_enabled() &&
         isolate_->optimizing_compiler_thread()->IsQueuedForOSR(function)) {
       // Do not attempt regular recompilation if we already queued this for OSR.
       // TODO(yangguo): This is necessary so that we don't install optimized