Add first version of tailing logs on Android

tools/cordova/run-targets.js

@@ -101,5 +101,45 @@ export class AndroidRunTarget extends CordovaRunTarget {
 
   async start(cordovaProject) {
     await cordovaProject.run(this.platform, this.isDevice);
+
+    this.tailLogs(cordovaProject).done();
+  }
+
+  async checkPlatformRequirementsAndSetEnv(cordovaProject) {
+    // Cordova Android is fairly good at applying various heuristics to find
+    // suitable values for JAVA_HOME and ANDROID_HOME, and to augment the PATH
+    // with those variables.
+    // Unfortunately, this is intertwined with checking requirements, so the
+    // only way to get access to this functionality is to run check_reqs and
+    // let it modify process.env
+    const check_reqs = require(files.pathJoin(
+      cordovaProject.projectRoot, 'platforms', this.platform,
+      'cordova', 'lib', 'check_reqs'));
+    // We can't use check_reqs.run() because that will print the values of
+    // JAVA_HOME and ANDROID_HOME to stdout.
+    await Promise.all([check_reqs.check_java(),
+      check_reqs.check_android().then(check_reqs.check_android_target)]);
+  }
+
+  async tailLogs(cordovaProject) {
+    cordovaProject.runCommands(`tailing logs for ${this.displayName}`, async () => {
+      await this.checkPlatformRequirementsAndSetEnv(cordovaProject);
+
+      // XXX This only works if we have at most one device or one emulator
+      // connected. We should find a way to get the target ID from run and use
+      // it instead of -d or -e.
+      const target = this.isDevice ? "-d" : "-e";
+
+      // Clear logs
+      await execFileAsync('adb', [target, 'logcat', '-c']);
+
+      const filterExpressions = ['CordovaLog:I', 'chromium:I',
+        'SystemWebViewClient:I', '*:S'];
+
+      // Asynchronously start tailing logs to stdout
+      execFileAsync('adb', [target, 'logcat',
+        ...filterExpressions],
+        { stdio: 'inherit' });
+    });
   }
 }