Display content_shell error messages.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py
index d97e82c32f6ef8e28e4a60058c708c7c2040e63b..7a383b301d4a2127879b385f0573b056e9060730 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/driver.py
@@ -332,9 +332,11 @@ class Driver(object):
     def _wait_for_server_process_output(self, server_process, deadline, text):
         output = ''
         line = server_process.read_stdout_line(deadline)
+        output += server_process.pop_all_buffered_stderr()
         while not server_process.timed_out and not server_process.has_crashed() and not text in line.rstrip():
             output += line
             line = server_process.read_stdout_line(deadline)
+            output += server_process.pop_all_buffered_stderr()
 
         if server_process.timed_out or server_process.has_crashed():
             _log.error('Failed to start the %s process: \n%s', server_process.name(), output)