[Telemetry] Fix NotImplementedError exceptions.

tools/telemetry/telemetry/core/backends/android_app_backend.py

Index: tools/telemetry/telemetry/core/backends/android_app_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/android_app_backend.py b/tools/telemetry/telemetry/core/backends/android_app_backend.py
index ddd84688b458fc971aafe2c967044cc2f2f6b5c2..ac38ae13bd3505bc37386569ffd19ff41a81fbc4 100644
--- a/tools/telemetry/telemetry/core/backends/android_app_backend.py
+++ b/tools/telemetry/telemetry/core/backends/android_app_backend.py
@@ -8,3 +8,22 @@ from telemetry.core.backends import app_backend
 class AndroidAppBackend(app_backend.AppBackend):
   def __init__(self):
     super(AndroidAppBackend, self).__init__()
+
+  @property
+  def pid(self):
+    raise NotImplementedError
+
+  def Start(self):
+    raise NotImplementedError
+
+  def Close(self):
+    raise NotImplementedError
+
+  def IsAppRunning(self):
+    raise NotImplementedError
+
+  def GetStandardOutput(self):
+    raise NotImplementedError
+
+  def GetStackTrace(self):
+    raise NotImplementedError