Add a helper for implementing Promise-valued properties.

Source/bindings/core/v8/v8.gypi

Index: Source/bindings/core/v8/v8.gypi
diff --git a/Source/bindings/core/v8/v8.gypi b/Source/bindings/core/v8/v8.gypi
index 1356aadcb760c39a24d3fec41044cf4725412d5a..a16027d0b42976608b7919c1c34af0bafeb885bb 100644
--- a/Source/bindings/core/v8/v8.gypi
+++ b/Source/bindings/core/v8/v8.gypi
@@ -74,6 +74,10 @@
             'ScriptPromise.h',
             'ScriptPromiseResolver.cpp',
             'ScriptPromiseResolver.h',
+            'ScriptPromiseProperties.h',
+            'ScriptPromiseProperty.h',
+            'ScriptPromisePropertyBase.cpp',
+            'ScriptPromisePropertyBase.h',
             'ScriptRegexp.cpp',
             'ScriptRegexp.h',
             'ScriptSourceCode.h',
@@ -155,6 +159,7 @@
         ],
         'bindings_core_v8_unittest_files': [
             'ScriptPromiseTest.cpp',
+            'ScriptPromisePropertyTest.cpp',
         ],
     },
 }