Create symlink to adb in home dir right before device setup.

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_android_n6.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "tryserver.webrtc",
       "--builder",
       "android_n6",
@@ skipping 137 matching lines @@
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
   {
     "cmd": [
+      "python",
+      "-u",
+      "[SLAVE_BUILD]/src/build/symlink.py",
+      "-f",
+      "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools/adb",
+      "~/adb"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "create adb symlink"
+  },
+  {
+    "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/daemonizer.py",
       "--",
       "[SLAVE_BUILD]/src/build/android/adb_logcat_monitor.py",
       "[SLAVE_BUILD]/src/out/logcat"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "spawn_logcat_monitor"
@@ skipping 569 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]