[WIP] DevToolsClientBackend with tracing 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 2351e60e210ec303b5cf74c01b20544467bd5c49..927928541137f7516d6d0834924dbf13911fec86 100644
--- a/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
+++ b/tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
@@ -28,7 +28,7 @@ class TracingControllerBackend(object):
 
     if trace_options.enable_chrome_trace:
       browser_backend = self.running_browser_backends[0]
-      browser_backend.StartTracing(
+      browser_backend.devtools_client.StartChromeTracing(
           trace_options, category_filter.filter_string, timeout)
 
   def Stop(self):
@@ -38,6 +38,10 @@ class TracingControllerBackend(object):
     result = None
     if self._current_trace_options.enable_chrome_trace:
       browser_backend = self.running_browser_backends[0]
+      # TODO(chrishenry): This should be modified to
+      # browser_backend.devtools_client.StopTracing() when we move the
+      # logic in ChromeBrowserBackend.StopTracing to
+      # DevToolsClientBackend..
       result = browser_backend.StopTracing()
 
     self._current_trace_options = None
@@ -61,7 +65,8 @@ class TracingControllerBackend(object):
   def IsChromeTracingSupported(self):
     self._AssertOneBrowserBackend()
     browser_backend = self.running_browser_backends[0]
-    return browser_backend.supports_tracing
+    return (browser_backend.devtools_client.IsAlive() and
+            browser_backend.devtools_client.supports_tracing)
 
   @property
   def is_tracing_running(self):