internal/goexperiment: add Green Tea GC goexperiment

Change-Id: Ia3ea5290842d8eddfafad4882f5874a2aff03e94
Reviewed-on: https://go-review.googlesource.com/c/go/+/645935
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/internal/goexperiment/exp_greenteagc_off.go

@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.greenteagc
+
+package goexperiment
+
+const GreenTeaGC = false
+const GreenTeaGCInt = 0

src/internal/goexperiment/exp_greenteagc_on.go

@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.greenteagc
+
+package goexperiment
+
+const GreenTeaGC = true
+const GreenTeaGCInt = 1

src/internal/goexperiment/flags.go

@@ -126,4 +126,7 @@ type Flags struct {
 
 	// JSONv2 enables the json/v2 package.
 	JSONv2 bool
+
+	// GreenTeaGC enables the Green Tea GC implementation.
+	GreenTeaGC bool
 }