[Telemetry] Make prebuilt binary installation a little more robust.

tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py

Index: tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
index f956cedb4bbe931909a7d025754f823a49cfb28a..2758d05a8b3b106060c02b12b13322a6c3f6e48e 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
+++ b/tools/telemetry/telemetry/core/backends/chrome/android_browser_finder.py
@@ -225,16 +225,13 @@ def FindAllAvailableBrowsers(finder_options, logging=real_logging):
     if 'package:' + package in packages or b.HaveLocalAPK():
       possible_browsers.append(b)
 
-  # See if the "forwarder" is installed -- we need this to host content locally
-  # but make it accessible to the device.
-  if (len(possible_browsers) and not finder_options.android_rndis and
-      not adb_commands.HasForwarder()):
-    logging.warn('telemetry detected an android device. However,')
-    logging.warn('Chrome\'s port-forwarder app is not available.')
-    logging.warn('Falling back to prebuilt binaries, but to build locally: ')
-    logging.warn('  ninja -C out/Release android_tools')
-    logging.warn('')
-    logging.warn('')
-    if not adb_commands.SetupPrebuiltTools(device):
+  if possible_browsers:
+    installed_prebuilt_tools = adb_commands.SetupPrebuiltTools(adb)
+    if not installed_prebuilt_tools:
+      logging.error(
+          'Android device detected, however prebuilt android tools could not '
+          'be used. To run on Android you must build them first:\n'
+          '  $ ninja -C out/Release android_tools')
       return []
+
   return possible_browsers