Take non-default browser target location into account when attaching to it.

telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py

Index: telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
diff --git a/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py b/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
index 3e58bf9fa6db410d29a662baf0e645c80ebb6b75..2133ca53af3a7e4c13c08e1e0477c0b3e4285132 100644
--- a/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
+++ b/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py
@@ -34,6 +34,7 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
         browser_options=browser_options,
         tab_list_backend=tab_list_backend.TabListBackend)
     self._port = None
+    self._browser_target = None
 
     self._supports_tab_control = supports_tab_control
     self._devtools_client = None
@@ -134,7 +135,9 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
 
   def HasBrowserFinishedLaunching(self):
     assert self._port, 'No DevTools port info available.'
-    return devtools_client_backend.IsDevToolsAgentAvailable(self._port, self)
+    return devtools_client_backend.IsDevToolsAgentAvailable(
+        self._port,
+        self._browser_target, self)
 
   def _InitDevtoolsClientBackend(self, remote_devtools_port=None):
     """ Initiate the devtool client backend which allow browser connection
@@ -147,7 +150,8 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
     assert not self._devtools_client, (
         'Devtool client backend cannot be init twice')
     self._devtools_client = devtools_client_backend.DevToolsClientBackend(
-        self._port, remote_devtools_port or self._port, self)
+        self._port, self._browser_target,
+        remote_devtools_port or self._port, self)
 
   def _WaitForBrowserToComeUp(self):
     """ Wait for browser to come up. """