Extend --trace-gc to output amount of memory reserved for V8 heap.

src/heap.h

 // 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 2427 matching lines @@
 
  private:
   // Returns a string matching the collector.
   const char* CollectorString();
 
   // Returns size of object in heap (in MB).
   double SizeOfHeapObjects() {
     return (static_cast<double>(HEAP->SizeOfObjects())) / MB;
   }
 
-  double start_time_;  // Timestamp set in the constructor.
-  intptr_t start_size_;  // Size of objects in heap set in constructor.
-  GarbageCollector collector_;  // Type of collector.
+  // Timestamp set in the constructor.
+  double start_time_;
+
+  // Size of objects in heap set in constructor.
+  intptr_t start_object_size_;
+
+  // Size of memory allocated from OS set in constructor.
+  intptr_t start_memory_size_;
+
+  // Type of collector.
+  GarbageCollector collector_;
 
   // A count (including this one, e.g. the first collection is 1) of the
   // number of garbage collections.
   unsigned int gc_count_;
 
   // A count (including this one) of the number of full garbage collections.
   int full_gc_count_;
 
   // Amounts of time spent in different scopes during GC.
   double scopes_[Scope::kNumberOfScopes];
@@ skipping 228 matching lines @@
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG || LIVE_OBJECT_LIST
 
 } }  // namespace v8::internal
 
 #undef HEAP
 
 #endif  // V8_HEAP_H_