Merge array allocation and List._copyFromObjectArray to provide fast path for large arrays.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 2df010cf886b4b52c52abb00a606a26847fa418e..835fe406114c1a85f2c21df59d63500b5e587ae0 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -1601,6 +1601,13 @@ Definition* LoadFieldInstr::Canonicalize(FlowGraph* flow_graph) {
       return call->ArgumentAt(0);
     }
   }
+
+  CreateArrayInstr* create_array = instance()->definition()->AsCreateArray();
+  if ((create_array != NULL) &&
+      (recognized_kind() == MethodRecognizer::kObjectArrayLength)) {
+    return create_array->num_elements()->definition();
+  }
+
   // For arrays with guarded lengths, replace the length load
   // with a constant.
   LoadFieldInstr* load_array = instance()->definition()->AsLoadField();