Introduce a class encapsulating arguments descriptor arrays.

runtime/vm/code_patcher_x64_test.cc

Index: runtime/vm/code_patcher_x64_test.cc
diff --git a/runtime/vm/code_patcher_x64_test.cc b/runtime/vm/code_patcher_x64_test.cc
index 2cfd5987f71c276edb7b4477ee7b771fe7ab01ce..5476ec48666f0f5d42f1a5eac46ff29eee5cb7fe 100644
--- a/runtime/vm/code_patcher_x64_test.cc
+++ b/runtime/vm/code_patcher_x64_test.cc
@@ -56,11 +56,13 @@ ASSEMBLER_TEST_GENERATE(IcDataAccess, assembler) {
                     true, false, false, false, owner_class, 0));
 
   const String& target_name = String::Handle(String::New("targetFunction"));
-  ICData& ic_data = ICData::ZoneHandle(
-      ICData::New(function, target_name, 15, 1));
+  const ICData& ic_data =
+      ICData::ZoneHandle(ICData::New(function, target_name, 15, 1));
+  const Array& arg_descriptor =
+      Array::ZoneHandle(ArgumentsDescriptor::New(1, Array::Handle()));
 
   __ LoadObject(RBX, ic_data);
-  __ LoadObject(R10, DartEntry::ArgumentsDescriptor(1, Array::Handle()));
+  __ LoadObject(R10, arg_descriptor);
   ExternalLabel target_label(
       "InlineCache", StubCode::OneArgCheckInlineCacheEntryPoint());
   __ call(&target_label);