Make EqualsIgnoringPrivateKey work with mixin applications.

runtime/vm/object_test.cc

Index: runtime/vm/object_test.cc
diff --git a/runtime/vm/object_test.cc b/runtime/vm/object_test.cc
index a9fa357ca9efd6d2d2e3a71afdd2715fb1d5d137..a67649f6102d9084cf17fd03924dd12bc77080eb 100644
--- a/runtime/vm/object_test.cc
+++ b/runtime/vm/object_test.cc
@@ -3191,6 +3191,16 @@ ISOLATE_UNIT_TEST_CASE(EqualsIgnoringPrivate) {
   bare_name = OneByteString::New("food");
   EXPECT(!String::EqualsIgnoringPrivateKey(mangled_name, bare_name));
 
+  // Private mixin application match.
+  mangled_name = OneByteString::New("_M1@12345&_M2@12345&_M3@12345");
+  bare_name = OneByteString::New("_M1&_M2&_M3");
+  EXPECT(String::EqualsIgnoringPrivateKey(mangled_name, bare_name));
+
+  // Private mixin application mismatch.
+  mangled_name = OneByteString::New("_M1@12345&_M2@12345&_M3@12345");
+  bare_name = OneByteString::New("_M1&_M2&_M4");
+  EXPECT(!String::EqualsIgnoringPrivateKey(mangled_name, bare_name));
+
   // Private constructor match.
   mangled_name = OneByteString::New("foo@12345.");
   bare_name = OneByteString::New("foo.");