Make it possible to configure synthetic delays through Devtools

tools/telemetry/telemetry/core/backends/browser_backend.py

Index: tools/telemetry/telemetry/core/backends/browser_backend.py
diff --git a/tools/telemetry/telemetry/core/backends/browser_backend.py b/tools/telemetry/telemetry/core/backends/browser_backend.py
index ac46b4f8b884001e190e2ee28185d20e9d1b8b51..8fafa411ab5f7e7bfa64bf58a09e0f37d2ca6c4d 100644
--- a/tools/telemetry/telemetry/core/backends/browser_backend.py
+++ b/tools/telemetry/telemetry/core/backends/browser_backend.py
@@ -70,6 +70,14 @@ class BrowserBackend(object):
   def StopTracing(self):
     raise NotImplementedError()
 
+  @property
+  def supports_synthetic_delays(self):
+    return False
+
+  def ConfigureSyntheticDelays(self, delays,
+      timeout=web_contents.DEFAULT_WEB_CONTENTS_TIMEOUT):
+    raise NotImplementedError()
+
   def GetRemotePort(self, _):
     return util.GetUnreservedAvailableLocalPort()