Enable 3rd party cookies in TestRunner::Reset()

The default for 3rd-party cookies in content shell has
been changes from "deny" to "allow" by
https://chromium-review.googlesource.com/1196547
However, we still reset it to "deny" when resetting
the TestRunner between tests, which causes inconsistent
behavior for tests that depend on default value.

Bug: 890000
Change-Id: If85535e617eb884e5fdd64c928d558f9fa84bb29
Reviewed-on: https://chromium-review.googlesource.com/1250165Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595606}

content/shell/test_runner/test_runner.cc

@@ -1565,7 +1565,7 @@ void TestRunner::Reset() {
     delegate_->SetDatabaseQuota(kDefaultDatabaseQuota);
     delegate_->SetDeviceColorSpace("reset");
     delegate_->SetDeviceScaleFactor(GetDefaultDeviceScaleFactor());
-    delegate_->SetBlockThirdPartyCookies(true);
+    delegate_->SetBlockThirdPartyCookies(false);
     delegate_->SetLocale("");
     delegate_->UseUnfortunateSynchronousResizeMode(false);
     delegate_->DisableAutoResizeMode(blink::WebSize());