internal/trace: skip tests for alloc/free experiment by default

These tests are just too flaky and I don't have the time to fix them
right now. I also am thinking to just change how trace experiments work,
so it may not be worth taking the time to fix them.

For #70838.

Change-Id: Ia896215a0cbeccac99b73fefc836088f43530849
Reviewed-on: https://go-review.googlesource.com/c/go/+/728122
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/internal/trace/reader_test.go

@@ -20,6 +20,7 @@ import (
 var (
 	logEvents  = flag.Bool("log-events", false, "whether to log high-level events; significantly slows down tests")
 	dumpTraces = flag.Bool("dump-traces", false, "dump traces even on success")
+	allocFree  = flag.Bool("alloc-free", false, "run alloc/free trace experiment tests")
 )
 
 func TestReaderGolden(t *testing.T) {

src/internal/trace/trace_test.go

@@ -697,6 +697,9 @@ func testTraceProg(t *testing.T, progName string, extra func(t *testing.T, trace
 		runTest(t, true, "")
 	})
 	t.Run("AllocFree", func(t *testing.T) {
+		if !*allocFree {
+			t.Skip("skipping trace alloc/free tests by default; too flaky (see go.dev/issue/70838)")
+		}
 		if testing.Short() {
 			t.Skip("skipping trace alloc/free tests in short mode")
 		}