[Telemetry] Properly chose an available device port.

Previously, we'd start WPR on an available host port and then just
assume that the same port was free on the device -- oops.

Now, we pass 0 to the forwarder for the device port so that it chooses
an available port, and then read back the port that it chose to use
for the mapping.

I believe this fixes a major case of device forwarder flake.

BUG=421599
TBR=slamm@chromium.org

Review URL: https://codereview.chromium.org/640133002

Cr-Commit-Position: refs/heads/master@{#299319}

tools/telemetry/telemetry/core/forwarders/__init__.py

@@ -33,7 +33,9 @@ class Forwarder(object):
 
   def __init__(self, port_pairs):
     assert port_pairs.http, 'HTTP port mapping is required.'
-    self._port_pairs = port_pairs
+    self._port_pairs = PortPairs(*[
+        PortPair(p.local_port, p.remote_port or p.local_port)
+        if p else None for p in port_pairs])
 
   @property
   def host_port(self):
@@ -43,6 +45,10 @@ class Forwarder(object):
   def host_ip(self):
     return '127.0.0.1'
 
+  @property
+  def port_pairs(self):
+    return self._port_pairs
+
   @property
   def url(self):
     assert self.host_ip and self.host_port

tools/telemetry/telemetry/core/forwarders/android_forwarder.py

@@ -54,13 +54,19 @@ class AndroidForwarder(forwarders.Forwarder):
   def __init__(self, adb, port_pairs):
     super(AndroidForwarder, self).__init__(port_pairs)
     self._device = adb.device()
-    forwarder.Forwarder.Map([p for p in port_pairs if p], self._device)
+    forwarder.Forwarder.Map([(p.remote_port, p.local_port)
+                             for p in port_pairs if p], self._device)
+    self._port_pairs = forwarders.PortPairs(*[
+        forwarders.PortPair(
+            p.local_port,
+            forwarder.Forwarder.DevicePortForHostPort(p.local_port))
+        if p else None for p in port_pairs])
     # TODO(tonyg): Verify that each port can connect to host.
 
   def Close(self):
     for port_pair in self._port_pairs:
       if port_pair:
-        forwarder.Forwarder.UnmapDevicePort(port_pair.local_port, self._device)
+        forwarder.Forwarder.UnmapDevicePort(port_pair.remote_port, self._device)
     super(AndroidForwarder, self).Close()
 
 

tools/telemetry/telemetry/core/wpr_server.py

@@ -47,10 +47,10 @@ class ReplayServer(object):
     # Assign the forwarder port pairs back to the browser_backend.
     #     The port pairs are used to set up the application.
     #     The chrome_browser_backend uses the remote ports to set browser flags.
-    browser_backend.wpr_port_pairs = self._ForwarderPortPairs(
+    port_pairs = self._ForwarderPortPairs(
         started_ports, browser_backend.wpr_port_pairs)
-    self._forwarder = browser_backend.forwarder_factory.Create(
-        browser_backend.wpr_port_pairs)
+    self._forwarder = browser_backend.forwarder_factory.Create(port_pairs)
+    browser_backend.wpr_port_pairs = self._forwarder.port_pairs
 
   @staticmethod
   def _ForwarderPortPairs(started_ports, wpr_port_pairs):
@@ -70,8 +70,8 @@ class ReplayServer(object):
       a forwarders.PortPairs instance used to create the forwarder.
     """
     local_http_port, local_https_port, local_dns_port = started_ports
-    remote_http_port = wpr_port_pairs.http.remote_port or local_http_port
-    remote_https_port = wpr_port_pairs.https.remote_port or local_https_port
+    remote_http_port = wpr_port_pairs.http.remote_port
+    remote_https_port = wpr_port_pairs.https.remote_port
     http_port_pair = forwarders.PortPair(local_http_port, remote_http_port)
     https_port_pair = forwarders.PortPair(local_https_port, remote_https_port)
     if wpr_port_pairs.dns is None:

tools/telemetry/telemetry/core/wpr_server_unittest.py

@@ -13,8 +13,8 @@ class ForwarderPortPairsTest(unittest.TestCase):
   def testNoRemotePortsGivesLocalToLocal(self):
     started_ports = (8080, 8443, None)
     wpr_port_pairs = forwarders.PortPairs(
-        http=forwarders.PortPair(0, 0),
-        https=forwarders.PortPair(0, 0),
+        http=forwarders.PortPair(0, 8080),
+        https=forwarders.PortPair(0, 8443),
         dns=None)
     expected_port_pairs = forwarders.PortPairs(
         http=forwarders.PortPair(8080, 8080),