[Telemetry] Refactor Chrome devtools tracing

tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py

Index: tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py
diff --git a/tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py b/tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py
index b1ef7f6331348d0b16c26300542a69383a036999..759278b6e8584523a0969423e2087d42139efb9d 100644
--- a/tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py
+++ b/tools/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py
@@ -5,11 +5,13 @@
 import os
 import shutil
 import stat
+import sys
 import tempfile
+import traceback
 
 from telemetry.internal.platform import tracing_agent
 from telemetry.internal.platform.tracing_agent import (
-    chrome_devtools_tracing_backend)
+    chrome_tracing_devtools_manager)
 
 _DESKTOP_OS_NAMES = ['linux', 'mac', 'win']
 
@@ -19,12 +21,17 @@ _CHROME_TRACE_CONFIG_DIR_ANDROID = '/data/local/'
 _CHROME_TRACE_CONFIG_FILE_NAME = 'chrome-trace-config.json'
 
 
+class ChromeTracingStartedError(Exception):
+  pass
+
+
+class ChromeTracingStoppedError(Exception):
+  pass
+
+
 class ChromeTracingAgent(tracing_agent.TracingAgent):
   def __init__(self, platform_backend):
     super(ChromeTracingAgent, self).__init__(platform_backend)
-    self._chrome_devtools_tracing_backend = (
-      chrome_devtools_tracing_backend.ChromeDevtoolsTracingBackend(
-        platform_backend))
     self._trace_config_file = None
 
   @property
@@ -32,21 +39,45 @@ class ChromeTracingAgent(tracing_agent.TracingAgent):
     return self._trace_config_file
 
   @classmethod
-  def RegisterDevToolsClient(cls, devtools_client_backend, platform_backend):
-    (chrome_devtools_tracing_backend.ChromeDevtoolsTracingBackend
-        .RegisterDevToolsClient(devtools_client_backend, platform_backend))
-
-  @classmethod
   def IsSupported(cls, platform_backend):
-    return (chrome_devtools_tracing_backend.ChromeDevtoolsTracingBackend
-      .IsSupported(platform_backend))
+    return chrome_tracing_devtools_manager.IsSupported(platform_backend)
 
   def Start(self, trace_options, category_filter, timeout):
-    return self._chrome_devtools_tracing_backend.Start(
-        trace_options, category_filter, timeout)
+    if not trace_options.enable_chrome_trace:
+      return False
+    devtools_clients = (chrome_tracing_devtools_manager
+        .GetActiveDevToolsClients(self._platform_backend))
+    if not devtools_clients:
+      return False
+    for client in devtools_clients:
+      if client.is_tracing_running:
+        raise ChromeTracingStartedError(
+            'Tracing is already running on devtools at port %s on platform'
+            'backend %s.' % (client.remote_port, self._platform_backend))
+      client.StartChromeTracing(
+          trace_options, category_filter.filter_string, timeout)
+    return True
 
   def Stop(self, trace_data_builder):
-    self._chrome_devtools_tracing_backend.Stop(trace_data_builder)
+    # We get all DevTools clients including the stale ones, so that we get an
+    # exception if there is a stale client. This is because we will potentially
+    # lose data if there is a stale client.
+    devtools_clients = (chrome_tracing_devtools_manager
+        .GetDevToolsClients(self._platform_backend))
+    raised_execption_messages = []
+    for client in devtools_clients:
+      try:
+        client.StopChromeTracing(trace_data_builder)
+      except Exception:
+        raised_execption_messages.append(
+          'Error when trying to stop tracing on devtools at port %s:\n%s'
+          % (client.remote_port,
+             ''.join(traceback.format_exception(*sys.exc_info()))))
+
+    if raised_execption_messages:
+      raise ChromeTracingStoppedError(
+          'Exceptions raised when trying to stop devtool tracing\n:' +
+          '\n'.join(raised_execption_messages))
 
   def _CreateTraceConfigFile(self, config):
     assert not self._trace_config_file