Make it possible to configure synthetic delays through Devtools

tools/telemetry/telemetry/page/actions/set_synthetic_delays.py

Index: tools/telemetry/telemetry/page/actions/set_synthetic_delays.py
diff --git a/tools/telemetry/telemetry/page/actions/set_synthetic_delays.py b/tools/telemetry/telemetry/page/actions/set_synthetic_delays.py
new file mode 100644
index 0000000000000000000000000000000000000000..6a3e1cb61f0f0a44c10568738d8d18f9196959f1
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+++ b/tools/telemetry/telemetry/page/actions/set_synthetic_delays.py
@@ -0,0 +1,30 @@
+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+from telemetry.page.actions import page_action
+
+class SetSyntheticDelaysAction(page_action.PageAction):
+  """Allows pages to configure synthetic delays in various parts of the browser.
+
+  Synthetic delays can be used to reliably simulate heavy workloads in different
+  parts of the input and graphics pipeline. For more information see
+  base/debug/trace_event_synthetic_delay.h. Prior to configuring the new delays,
+  all existing delays are reset.
+
+  Args:
+    delays: A dictionary of delays to configure. Each delay can have the
+            following properties:
+            target_duration: How many seconds the delay point should execute.
+            mode: Delay mode; one of 'static', 'oneshot' or 'alternating'.
+  """
+  def __init__(self, attributes=None):
+    super(SetSyntheticDelaysAction, self).__init__(attributes)
+
+  def WillRunAction(self, page, tab):
+    # Fail if browser doesn't support synthetic delays.
+    if not tab.browser.supports_synthetic_delays:
+      raise page_action.PageActionNotSupported(
+          'Synthetic delays not supported for this browser')
+
+  def RunAction(self, page, tab, previous_action):
+    tab.browser.ConfigureSyntheticDelays(getattr(self, 'delays', {}), 10)