[turbofan] Introduce JSCallForwardVarargs operator.

src/ia32/interface-descriptors-ia32.cc

Index: src/ia32/interface-descriptors-ia32.cc
diff --git a/src/ia32/interface-descriptors-ia32.cc b/src/ia32/interface-descriptors-ia32.cc
index cef6449ca0775097973cb57d265d89a3fda2768a..6535baac9647ad26321cde7e40ec24c0b1507595 100644
--- a/src/ia32/interface-descriptors-ia32.cc
+++ b/src/ia32/interface-descriptors-ia32.cc
@@ -178,6 +178,13 @@ void CallTrampolineDescriptor::InitializePlatformSpecific(
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  // ecx : start index (to support rest parameters)
+  // edi : the target to call
+  Register registers[] = {edi, ecx};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
 
 void ConstructStubDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {