Try fixing telemetry on CrOS

telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py

Index: telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py
diff --git a/telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py b/telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py
index 07c5af041c6e3c7060b2ea0401a04803c26039f1..1f200bad0ddbc39e665dcf33c761cb949bae34d9 100644
--- a/telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py
+++ b/telemetry/telemetry/internal/backends/chrome/cros_browser_backend.py
@@ -6,11 +6,9 @@ import logging
 import os
 
 from telemetry.core import exceptions
-from telemetry.core import util
 from telemetry import decorators
 from telemetry.internal.backends.chrome import chrome_browser_backend
 from telemetry.internal.backends.chrome import misc_web_contents_backend
-from telemetry.internal import forwarders
 
 import py_utils
 
@@ -25,9 +23,8 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
     # Initialize fields so that an explosion during init doesn't break in Close.
     self._cri = cri
     self._is_guest = is_guest
-    self._forwarder = None
-    self._remote_debugging_port = self._cri.GetRemotePort()
-    self._port = self._remote_debugging_port
+    self._port = None
+    self._browser_target = None
 
     extensions_to_load = browser_options.extensions_to_load
 
@@ -53,6 +50,33 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
   def log_file_path(self):
     return None
 
+  def HasBrowserFinishedLaunching(self):
+    # Start DevTools on an ephemeral port and wait for the well-known file
+    # containing the port number to exist.
+    port_file = os.path.join(self.profile_directory, 'DevToolsActivePort')
+    if not os.path.isfile(port_file):
+      # File isn't ready yet. Return false. Will retry.
+      return False
+    # Attempt to avoid reading the file until it's populated.
+    got_port = False
+    try:
+      if os.stat(port_file).st_size > 0:
+        with open(port_file) as f:
+          port_target = f.read().split('\n')
+          self._port = int(port_target[0])
+          if len(port_target) > 1 and port_target[1]:
+            self._browser_target = port_target[1]
+          logging.info('Discovered ephemeral port %s', self._port)
+          logging.info('Browser target: %s', self._browser_target)
+          got_port = True
+    except Exception:
+      # Both stat and open can throw exceptions.
+      pass
+    if not got_port:
+      # File isn't ready yet. Return false. Will retry.
+      return False
+    return super(CrOSBrowserBackend, self).HasBrowserFinishedLaunching()
+
   def GetBrowserStartupArgs(self):
     args = super(CrOSBrowserBackend, self).GetBrowserStartupArgs()
 
@@ -68,7 +92,7 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
         '--enable-smooth-scrolling',
         '--enable-threaded-compositing',
         # Allow devtools to connect to chrome.
-        '--remote-debugging-port=%i' % self._remote_debugging_port,
+        '--remote-debugging-port=0',
         # Open a maximized window.
         '--start-maximized',
         # Disable system startup sound.
@@ -131,18 +155,10 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
     logging.info(' '.join(args))
     self._cri.RunCmdOnDevice(args)
 
-    if not self._cri.local:
-      # TODO(crbug.com/404771): Move port forwarding to network_controller.
-      self._port = util.GetUnreservedAvailableLocalPort()
-      self._forwarder = self._platform_backend.forwarder_factory.Create(
-          forwarders.PortPair(self._port, self._remote_debugging_port),
-          use_remote_port_forwarding=False)
-
     # Wait for new chrome and oobe.
     py_utils.WaitFor(lambda: pid != self.pid, 15)
     self._WaitForBrowserToComeUp()
-    self._InitDevtoolsClientBackend(
-        remote_devtools_port=self._remote_debugging_port)
+    self._InitDevtoolsClientBackend()
     py_utils.WaitFor(lambda: self.oobe_exists, 30)
 
     if self.browser_options.auto_login:
@@ -186,10 +202,6 @@ class CrOSBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
 
     py_utils.WaitFor(lambda: not self._IsCryptohomeMounted(), 180)
 
-    if self._forwarder:
-      self._forwarder.Close()
-      self._forwarder = None
-
     if self._cri:
       for e in self._extensions_to_load:
         self._cri.RmRF(os.path.dirname(e.local_path))