Disable loading.mobile on Nexus6 WebView

https://crrev.com/2558743002 fixed loading.mobile on Nexus5 WebView and
page_cycler_v2 on Nexus5/Nexus6 WebView, but loading.mobile on Nexus6
WebView is still failing.

BUG=676612
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.perf:linux_perf_cq;master.tryserver.chromium.perf:mac_retina_perf_cq;master.tryserver.chromium.perf:winx64_10_perf_cq

Review-Url: https://codereview.chromium.org/2613153005
Cr-Commit-Position: refs/heads/master@{#441868}

tools/perf/benchmarks/loading.py

@@ -30,6 +30,12 @@ class LoadingMobile(perf_benchmark.PerfBenchmark):
     if possible_browser.browser_type == 'reference':
       return True
 
+    # crbug.com/676612
+    if ((possible_browser.platform.GetDeviceTypeName() == 'Nexus 6' or
+         possible_browser.platform.GetDeviceTypeName() == 'AOSP on Shamu') and
+        possible_browser.browser_type == 'android-webview'):
+      return True
+
     return False
 
   @classmethod