Add support in Telemetry for specifying exact Android APK

tools/telemetry/telemetry/unittest_util/system_stub.py

Index: tools/telemetry/telemetry/unittest_util/system_stub.py
diff --git a/tools/telemetry/telemetry/unittest_util/system_stub.py b/tools/telemetry/telemetry/unittest_util/system_stub.py
index 25bc8412b3ea494bae1f97fc6ec1f22c3a3b4203..2d2283e91574637da9db09fb61e129ee929d3388 100644
--- a/tools/telemetry/telemetry/unittest_util/system_stub.py
+++ b/tools/telemetry/telemetry/unittest_util/system_stub.py
@@ -121,6 +121,7 @@ class AdbCommandsModuleStub(object):
 
   def __init__(self):
     self.attached_devices = []
+    self.apk_package_name = None
     self.adb_device = AdbDevice()
 
     def AdbCommandsStubConstructor(device=None):
@@ -131,6 +132,9 @@ class AdbCommandsModuleStub(object):
   def IsAndroidSupported():
     return True
 
+  def GetPackageName(self, _):
+    return self.apk_package_name
+
   def GetAttachedDevices(self):
     return self.attached_devices