Fix crash during GC in gen_snapshot:

runtime/vm/object_store.cc

Index: runtime/vm/object_store.cc
===================================================================
--- runtime/vm/object_store.cc	(revision 40787)
+++ runtime/vm/object_store.cc	(working copy)
@@ -25,8 +25,12 @@
     int_type_(Type::null()),
     integer_implementation_class_(Class::null()),
     smi_class_(Class::null()),
+    smi_type_(Type::null()),
     mint_class_(Class::null()),
+    mint_type_(Type::null()),
+    bigint_class_(Class::null()),
     double_class_(Class::null()),
+    double_type_(Type::null()),
     float32x4_type_(Type::null()),
     int32x4_type_(Type::null()),
     float64x2_type_(Type::null()),
@@ -52,6 +56,9 @@
     async_library_(Library::null()),
     builtin_library_(Library::null()),
     core_library_(Library::null()),
+    collection_library_(Library::null()),
+    convert_library_(Library::null()),
+    internal_library_(Library::null()),
     isolate_library_(Library::null()),
     math_library_(Library::null()),
     mirrors_library_(Library::null()),
@@ -58,9 +65,11 @@
     native_wrappers_library_(Library::null()),
     root_library_(Library::null()),
     typed_data_library_(Library::null()),
+    profiler_library_(Library::null()),
     libraries_(GrowableObjectArray::null()),
     pending_classes_(GrowableObjectArray::null()),
     pending_functions_(GrowableObjectArray::null()),
+    pending_deferred_loads_(GrowableObjectArray::null()),
     resume_capabilities_(GrowableObjectArray::null()),
     sticky_error_(Error::null()),
     unhandled_exception_handler_(String::null()),
@@ -67,11 +76,15 @@
     empty_context_(Context::null()),
     stack_overflow_(Instance::null()),
     out_of_memory_(Instance::null()),
+    preallocated_unhandled_exception_(UnhandledException::null()),
     preallocated_stack_trace_(Stacktrace::null()),
     lookup_port_handler_(Function::null()),
     empty_uint32_array_(TypedData::null()),
     handle_message_function_(Function::null()),
     library_load_error_table_(Array::null()) {
+  for (RawObject** current = from(); current <= to(); current++) {
+    ASSERT(*current == Object::null());
+  }
 }