Reland again [Telemetry] Refactor Chrome devtools tracing

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

Index: tools/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py
diff --git a/tools/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py b/tools/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py
index a75a2af0bdf5d9cb26df5c884ac45129f366ba00..947a12abed3c262b0665d48f70510df40d4d90d9 100644
--- a/tools/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py
+++ b/tools/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py
@@ -8,10 +8,12 @@ import sys
 
 from telemetry.core import exceptions
 from telemetry import decorators
+from telemetry.internal.backends import browser_backend
 from telemetry.internal.backends.chrome_inspector import devtools_http
 from telemetry.internal.backends.chrome_inspector import inspector_backend
 from telemetry.internal.backends.chrome_inspector import tracing_backend
-from telemetry.internal.platform.tracing_agent import chrome_tracing_agent
+from telemetry.internal.platform.tracing_agent import (
+    chrome_tracing_devtools_manager)
 from telemetry.timeline import trace_data as trace_data_module
 
 
@@ -19,8 +21,13 @@ class TabNotFoundError(exceptions.Error):
   pass
 
 
-def IsDevToolsAgentAvailable(port):
+def IsDevToolsAgentAvailable(port, app_backend):
   """Returns True if a DevTools agent is available on the given port."""
+  if (isinstance(app_backend, browser_backend.BrowserBackend) and
+      app_backend.supports_tracing):
+    if not tracing_backend.IsInspectorWebsocketAvailable(port):
+      return False
+
   devtools_http_instance = devtools_http.DevToolsHttp(port)
   try:
     return _IsDevToolsAgentAvailable(devtools_http.DevToolsHttp(port))
@@ -66,13 +73,30 @@ class DevToolsClientBackend(object):
     self._devtools_context_map_backend = _DevToolsContextMapBackend(
         self._app_backend, self)
 
-    chrome_tracing_agent.ChromeTracingAgent.RegisterDevToolsClient(
-      self, self._app_backend.platform_backend)
+    if not self.supports_tracing:
+      return
+    self._tracing_backend = tracing_backend.TracingBackend(self._devtools_port)
+    chrome_tracing_devtools_manager.RegisterDevToolsClient(
+        self, self._app_backend.platform_backend)
 
   @property
   def remote_port(self):
     return self._remote_devtools_port
 
+  @property
+  def supports_tracing(self):
+    if not isinstance(self._app_backend, browser_backend.BrowserBackend):
+      return False
+    return self._app_backend.supports_tracing
+
+  @property
+  def is_tracing_running(self):
+    if not self.supports_tracing:
+      return False
+    if not self._tracing_backend:
+      return False
+    return self._tracing_backend.is_tracing_running
+
   def IsAlive(self):
     """Whether the DevTools server is available and connectable."""
     return _IsDevToolsAgentAvailable(self._devtools_http)
@@ -171,11 +195,14 @@ class DevToolsClientBackend(object):
     return self._devtools_context_map_backend
 
   def _CreateTracingBackendIfNeeded(self):
+    assert self.supports_tracing
     if not self._tracing_backend:
       self._tracing_backend = tracing_backend.TracingBackend(
           self._devtools_port)
 
   def IsChromeTracingSupported(self):
+    if not self.supports_tracing:
+      return False
     self._CreateTracingBackendIfNeeded()
     return self._tracing_backend.IsTracingSupported()