Change ITestClient to be similar to IChildProcessService.

base/test/android/java/src/org/chromium/base/ChildProcessConstants.java

Index: base/test/android/java/src/org/chromium/base/ChildProcessConstants.java
diff --git a/base/test/android/java/src/org/chromium/base/ChildProcessConstants.java b/base/test/android/java/src/org/chromium/base/ChildProcessConstants.java
new file mode 100644
index 0000000000000000000000000000000000000000..457c59cbb6f89608d041e57903bfa988b1ca51be
--- /dev/null
+++ b/base/test/android/java/src/org/chromium/base/ChildProcessConstants.java
@@ -0,0 +1,16 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+/**
+ * Constants to be used by child processes.
+ */
+public interface ChildProcessConstants {
+    // Key for the command line.
+    public static final String EXTRA_COMMAND_LINE = "org.chromium.base.extra.command_line";
+
+    // Key for the file descriptors that should be mapped in the child process..
+    public static final String EXTRA_FILES = "org.chromium.base.extra.extra_files";
+}