webkit_layout_test: Correctly deal with unicode on stacks

webkit_layout_tests will fail if there is a non-ascii character in the stack
dump. This CL encodes the stack dump to avoid that. Very probably there is some
other problem that is causing the stack to contain non-ascii characters, but at
this point we can't even tell what's the problem due to the crash (see the bug
for details).

Bug: 880246
Change-Id: I34c5582cc2d4bd98fb17053336e9084624df52a5
Reviewed-on: https://chromium-review.googlesource.com/1204015Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589464}

third_party/blink/tools/blinkpy/web_tests/port/android.py

@@ -793,7 +793,7 @@ class ChromiumAndroidDriver(driver.Driver):
                 stderr += '********* [%s] breakpad minidump %s:\n%s' % (
                     self._port.host.filesystem.basename(crash),
                     self._device.serial,
-                    stack)
+                    stack.encode('ascii', 'replace'))
 
         return super(ChromiumAndroidDriver, self)._get_crash_log(
             stdout, stderr, newer_than)