Make Android Perfetto tracing work on Windows.

Passing the binary data via adb doesn't quite work on Windows, so
encode the proto to base64 to make it go safely through adb.

core/os/android/adb/perfetto.go

@@ -16,8 +16,8 @@ package adb
 
 import (
 	"bufio"
-	"bytes"
 	"context"
+	"encoding/base64"
 	"io"
 	"strings"
 
@@ -56,8 +56,8 @@ func (b *binding) StartPerfettoTrace(ctx context.Context, config *perfetto_pb.Tr
 		}
 	})
 
-	process, err := b.Shell("perfetto", "-c", "-", "-o", out).
-		Read(bytes.NewReader(data)).
+	process, err := b.Shell("base64", "-d", "|", "perfetto", "-c", "-", "-o", out).
+		Read(strings.NewReader(base64.StdEncoding.EncodeToString(data))).
 		Capture(stdout, stdout).
 		Start(ctx)
 	if err != nil {