Relanding "Multiprocess test client: Android child process launcher rework."

testing/android/native_test/main_runner.cc

+// 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.
+
+#include <vector>
+
+#include "base/android/jni_array.h"
+#include "base/logging.h"
+#include "base/posix/global_descriptors.h"
+#include "jni/MainRunner_jni.h"
+
+extern int main(int argc, char** argv);
+
+namespace testing {
+namespace android {
+
+bool RegisterMainRunnerJni(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+static jint RunMain(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jclass>& jcaller,
+    const base::android::JavaParamRef<jobjectArray>& command_line,
+    const base::android::JavaParamRef<jintArray>& fds_to_map_keys,
+    const base::android::JavaParamRef<jintArray>& fds_to_map_fds) {
+  // Guards against process being reused.
+  // In most cases, running main again will cause problems (static variables,
+  // singletons, lazy instances won't be in the same state as a clean run).
+  static bool alreadyRun = false;
+  CHECK(!alreadyRun);
+  alreadyRun = true;
+
+  std::vector<int> keys;
+  base::android::JavaIntArrayToIntVector(env, fds_to_map_keys, &keys);
+  std::vector<int> fds;
+  base::android::JavaIntArrayToIntVector(env, fds_to_map_fds, &fds);
+  CHECK_EQ(keys.size(), fds.size());
+
+  for (size_t i = 0; i < keys.size(); i++) {
+    base::GlobalDescriptors::GetInstance()->Set(keys[i], fds[i]);
+  }
+
+  std::vector<std::string> cpp_command_line;
+  AppendJavaStringArrayToStringVector(env, command_line, &cpp_command_line);
+
+  std::vector<char*> c_command_line;
+  for (auto& entry : cpp_command_line) {
+    c_command_line.push_back(&entry[0]);
+  }
+
+  return main(c_command_line.size(), &c_command_line[0]);
+}
+
+}  // namespace android
+}  // namespace testing