[Telemetry] Fix up desktop_browser_finder on Linux

tools/telemetry/telemetry/testing/system_stub.py

Index: tools/telemetry/telemetry/testing/system_stub.py
diff --git a/tools/telemetry/telemetry/testing/system_stub.py b/tools/telemetry/telemetry/testing/system_stub.py
index 680f44298bf7b3c7636a7289fd9a0f7027deb110..18ae7dec51772758bc3e8e363adad5fb43b4b305 100644
--- a/tools/telemetry/telemetry/testing/system_stub.py
+++ b/tools/telemetry/telemetry/testing/system_stub.py
@@ -355,6 +355,14 @@ class OsModuleStub(object):
       return os.path.dirname(path)
 
     @staticmethod
+    def realpath(path):
+      return os.path.realpath(path)
+
+    @staticmethod
+    def split(path):
+      return os.path.split(path)
+
+    @staticmethod
     def splitext(path):
       return os.path.splitext(path)