Reland again [Telemetry] Refactor Chrome devtools tracing

tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py

Index: tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py
diff --git a/tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py b/tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py
index 52b501bff9ad3dd587af92046f52bcd0f3d9b246..dadf4a32f3bd92037ab58efd1660838bd77c0eaf 100644
--- a/tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py
+++ b/tools/telemetry/telemetry/internal/backends/chrome_inspector/tracing_backend.py
@@ -4,6 +4,7 @@
 
 import json
 import socket
+import sys
 import time
 
 from telemetry import decorators
@@ -32,6 +33,32 @@ class TracingUnexpectedResponseException(Exception):
   pass
 
 
+
+def IsInspectorWebsocketAvailable(port):
+  """Returns True if inspector websocket is available on the given port."""
+  inspector_websocket_instance = inspector_websocket.InspectorWebsocket()
+  try:
+    return _IsInspectorWebsocketAvailable(inspector_websocket_instance, port)
+  finally:
+    inspector_websocket_instance.Disconnect()
+
+def _IsInspectorWebsocketAvailable(inspector_websocket_instance, port):
+  try:
+    inspector_websocket_instance.Connect(
+        'ws://127.0.0.1:%i/devtools/browser' % port)
+  except websocket.WebSocketException:
+    return False
+  except socket.error:
+    return False
+  except Exception as e:
+    sys.stderr.write('Unidentified exception while checking if wesocket is'
+                     'available on port %i. Exception message: %s\n' %
+                     (port, e.message))
+    return False
+  else:
+    return True
+
+
 class _DevToolsStreamReader(object):
   def __init__(self, inspector_socket, stream_handle):
     self._inspector_websocket = inspector_socket