Chrome Version: 61.0.3124.3 (dev)
OS: Android L

testLoFiIfHeavyFastConnection is failing due to not sending a CPAT header in the request when the appropriate flags have been added.
  
Traceback (most recent call last):
  File "/usr/local/google/home/bustamante/cr-exp/src/tools/chrome_proxy/webdriver/lofi.py", line 93, in testLoFiIfHeavyFastConnection
    self.assertIn('chrome-proxy-accept-transform', response.request_headers)
AssertionError: 'chrome-proxy-accept-transform' not found in {u':path': u'/static/image1.png', u'accept-language': u'en-US,en;q=0.8', u'accept-encoding': u'gzip, deflate, br', u'chrome-proxy-ect': u'4G', u'accept': u'image/webp,image/apng,image/*,*/*;q=0.8', u':authority': u'check.googlezip.net', u':scheme': u'http', u'referer': u'http://check.googlezip.net/static/index.html', u':method': u'GET', u'user-agent': u'Mozilla/5.0 (Linux; Android 5.1.1; Nexus 7 Build/LMY49S) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3124.3 Safari/537.36', u'chrome-proxy': u's=CnEKEwir2MKe57HUAhUO8mIKHev3DKYSDAjx4_HJBRDYnLWEAxo3ChdoZWF2eV9wYWdlX3ByZXZpZXdzX2RldhIaZW5hYmxlX2hlYXZ5X3BhZ2VfcHJldmlld3MgASITaGVhdnlfcGFnZV9wcmV2aWV3cxJGMEQCIGE1p3McD_trj8j7N6GM2cySmQU394747TNJPy4l7LxUAiBDBkfNXEwR0i0UCEjlsBxs7nFqk2CJ2HWJmWNpyIj1gQ==, c=android, b=3124, p=3'}

It looks like the ECT is 4G despite having:

--force-fieldtrial-params=NetworkQualityEstimator.Enabled:force_effective_connection_type/Slow2G

Attempting to force it to Slow2G which would explain it.