[Telemetry] Add tracing_agent API.

tools/telemetry/telemetry/core/platform/tracing_controller_backend.py

Index: tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py b/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
index 3f5c18cb36d43d2c4ec803dbcf88d6abff689f03..980841f96fc9cde4048835508a16c41fad32b9e9 100644
--- a/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
+++ b/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
@@ -2,20 +2,37 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import os
+
+from telemetry.core import discover
+from telemetry.core import util
 from telemetry.core.platform import tracing_category_filter
 from telemetry.core.platform import tracing_options
+from telemetry.core.platform import tracing_agent
+from telemetry.core.platform.tracing_agent import chrome_tracing_agent
+from telemetry.core.platform.tracing_agent import display_tracing_agent
 from telemetry.timeline import trace_data as trace_data_module
 
 
+def _IterAllTracingAgentClasses():
+  tracing_agent_dir = os.path.dirname(os.path.join(
+      os.path.realpath(__file__), 'tracing_agent'))
+  return discover.DiscoverClasses(
+      tracing_agent_dir, util.GetTelemetryDir(),
+      tracing_agent.TracingAgent).itervalues()
+
+
 class TracingControllerBackend(object):
   def __init__(self, platform_backend):
     self._platform_backend = platform_backend
     self._current_trace_options = None
     self._current_category_filter = None
-    # A map from uniquely-identifying remote port (which may be the
-    # same as local port) to DevToolsClientBackend. There is no
-    # guarantee that the devtools agent is still alive.
-    self._devtools_clients_map = {}
+    self._current_chrome_tracing_agent = None
+    self._current_display_tracing_agent = None
+    self._supported_agents_classes = [
+        agent_classes for agent_classes in _IterAllTracingAgentClasses() if
+        agent_classes.IsSupported(platform_backend)]
+    self._active_agents_instances = []
 
   def Start(self, trace_options, category_filter, timeout):
     if self.is_tracing_running:
@@ -25,62 +42,38 @@ class TracingControllerBackend(object):
                       tracing_category_filter.TracingCategoryFilter)
     assert isinstance(trace_options,
                       tracing_options.TracingOptions)
+    assert len(self._active_agents_instances) == 0
 
     self._current_trace_options = trace_options
     self._current_category_filter = category_filter
-
-    if trace_options.enable_chrome_trace:
-      self._RemoveStaleDevToolsClient()
-      for _, devtools_client in self._devtools_clients_map.iteritems():
-        devtools_client.StartChromeTracing(
-            trace_options, category_filter.filter_string, timeout)
-
-    if trace_options.enable_platform_display_trace:
-      self._platform_backend.StartDisplayTracing()
-
-  def _RemoveStaleDevToolsClient(self):
-    """Removes DevTools clients that are no longer connectable."""
-    self._devtools_clients_map = {
-        port: client
-        for port, client in self._devtools_clients_map.iteritems()
-        if client.IsAlive()
-        }
+    # Hack: chrome tracing agent depends on the number of alive chrome devtools
+    # processes, rather platform, hence we add it to the list of supported
+    # agents here if it was not added.
+    if (chrome_tracing_agent.ChromeTracingAgent.IsSupported(
+        self._platform_backend) and
+        not chrome_tracing_agent.ChromeTracingAgent in
+        self._supported_agents_classes):
+      self._supported_agents_classes.append(
+          chrome_tracing_agent.ChromeTracingAgent)
+
+    for agent_class in self._supported_agents_classes:
+      agent = agent_class(self._platform_backend)
+      if agent.Start(trace_options, category_filter, timeout):
+        self._active_agents_instances.append(agent)
 
   def Stop(self):
     assert self.is_tracing_running, 'Can only stop tracing when tracing.'
-
     trace_data_builder = trace_data_module.TraceDataBuilder()
-    if self._current_trace_options.enable_chrome_trace:
-      for _, devtools_client in self._devtools_clients_map.iteritems():
-        # We do not check for stale DevTools client, 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_client.StopChromeTracing(trace_data_builder)
-
-    if self._current_trace_options.enable_platform_display_trace:
-      surface_flinger_trace_data = self._platform_backend.StopDisplayTracing()
-      trace_data_builder.AddEventsTo(
-          trace_data_module.SURFACE_FLINGER_PART, surface_flinger_trace_data)
-
+    for agent in self._active_agents_instances:
+      agent.Stop(trace_data_builder)
+    self._active_agents_instances = []
     self._current_trace_options = None
     self._current_category_filter = None
     return trace_data_builder.AsData()
 
-  def RegisterDevToolsClient(self, devtools_client_backend):
-    assert not self.is_tracing_running, (
-        'Cannot add new DevTools client when tracing is running.')
-    remote_port = str(devtools_client_backend.remote_port)
-    self._devtools_clients_map[remote_port] = devtools_client_backend
-
   def IsChromeTracingSupported(self):
-    self._RemoveStaleDevToolsClient()
-    for _, devtools_client in self._devtools_clients_map.iteritems():
-      if devtools_client.IsChromeTracingSupported():
-        return True
-    return False
-
-  def IsDisplayTracingSupported(self):
-    return self._platform_backend.IsDisplayTracingSupported()
+    return chrome_tracing_agent.ChromeTracingAgent.IsSupported(
+        self._platform_backend)
 
   @property
   def is_tracing_running(self):