Provide a mechanism for the embedder to set a TotalPhysicalMemory callback function.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 29ead298196a765e8ca856628bf301ef7d263a8a..47a795aa185d21c5aa48fdd98c19fcf9f6d27d22 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -102,6 +102,7 @@ void ThreadLocalTop::InitializeInternal() {
   thread_id_ = ThreadId::Invalid();
   external_caught_exception_ = false;
   failed_access_check_callback_ = NULL;
+  total_physical_memory_callback_ = NULL;
   save_context_ = NULL;
   catcher_ = NULL;
   top_lookup_result_ = NULL;
@@ -962,6 +963,12 @@ void Isolate::ReportFailedAccessCheck(JSObject* receiver, v8::AccessType type) {
 }
 
 
+void Isolate::SetTotalPhysicalMemoryCallback(
+      v8::TotalPhysicalMemoryCallback callback) {
+  thread_local_top()->total_physical_memory_callback_ = callback;
+}
+
+
 enum MayAccessDecision {
   YES, NO, UNKNOWN
 };