Support reusable boxes for Float32x4 fields

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 86063986655e6764289550255502ab488cf7ce3e..6da997089d4d7d24fa3748fea954ad62e0225418 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -26,6 +26,7 @@ DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(int, reoptimization_counter_threshold);
 DECLARE_FLAG(bool, enable_type_checks);
 DECLARE_FLAG(bool, eliminate_type_checks);
+DECLARE_FLAG(bool, enable_simd_inline);
 
 
 FlowGraphCompiler::~FlowGraphCompiler() {
@@ -43,6 +44,12 @@ bool FlowGraphCompiler::SupportsUnboxedMints() {
 }
 
 
+bool FlowGraphCompiler::SupportsUnboxedFloat32x4() {
+  return FLAG_enable_simd_inline;
+}
+
+
+
 bool FlowGraphCompiler::SupportsSinCos() {
   return true;
 }