adds log-ios and log-android cli commands

Summary:
solves first part of #8186
Closes https://github.com/facebook/react-native/pull/8352

Differential Revision: D3475905

Pulled By: mkonicek

fbshipit-source-id: 99f6aa15b92ba3192fa0b812d369bd7020469573

local-cli/logAndroid/logAndroid.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+const chalk = require('chalk');
+const child_process = require('child_process');
+const Promise = require('promise');
+
+/**
+ * Starts adb logcat
+ */
+function logAndroid() {
+  return new Promise((resolve, reject) => {
+    _logAndroid(resolve, reject);
+  });
+}
+
+function _logAndroid(resolve, reject) {
+  try {
+    const adbPath = process.env.ANDROID_HOME
+      ? process.env.ANDROID_HOME + '/platform-tools/adb'
+      : 'adb';
+
+    const adbArgs = ['logcat', '*:S', 'ReactNative:V', 'ReactNativeJS:V'];
+
+    console.log(chalk.bold(
+      `Starting the logger (${adbPath} ${adbArgs.join(' ')})...`
+    ));
+
+    const log = child_process.spawnSync(adbPath, adbArgs, {stdio: 'inherit'});
+
+    if (log.error !== null) {
+      throw log.error;
+    }
+
+  } catch (e) {
+    console.log(chalk.red(
+      'adb invocation failed. Do you have adb in your PATH?'
+    ));
+    reject();
+    return;
+  }
+}
+
+module.exports = logAndroid;