Provide a mechanism for dumping of heap profiles on predefined events.

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
diff --git a/runtime/vm/dart.cc b/runtime/vm/dart.cc
index d37c2d76ac2effa682675213c78c5428ba41f75e..bcac2b097330b881640db6f788488bfc1f7c151c 100644
--- a/runtime/vm/dart.cc
+++ b/runtime/vm/dart.cc
@@ -23,6 +23,8 @@
 
 namespace dart {
 
+DEFINE_FLAG(bool, heap_profile_initialize, false,
+            "Writes a heap profile on isolate initialization.");
 DECLARE_FLAG(bool, print_bootstrap);
 DECLARE_FLAG(bool, print_class_table);
 DECLARE_FLAG(bool, trace_isolates);
@@ -173,6 +175,10 @@ RawError* Dart::InitializeIsolate(const uint8_t* snapshot_buffer, void* data) {
     }
   }
 
+  if (FLAG_heap_profile_initialize) {
+    isolate->heap()->ProfileToFile("initialize");
+  }
+
   StubCode::Init(isolate);
   isolate->heap()->EnableGrowthControl();
   isolate->set_init_callback_data(data);