[AW] Make sure to expand accept languages (NS code path)

AcceptLanguageTests have been updated recently [1] to ensure expanded
accept languages header. This patch ensure this also happens in the
Network Service code path.

Impacted tests (fixed by this patch):
- org.chromium.android_webview.test.AcceptLanguageTest#testAcceptLanguage
- org.chromium.android_webview.test.AcceptLanguageTest#testAcceptLanguagesWithenUS

Note:
- verified on android_mojo bot (see tryjobs this patch)
- should also fix the [Mojo Android] fyi waterfall bot [2].

[1] https://crrev.com/c/1286936
[2] https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mojo%20Android

BUG=893561,841556

Change-Id: I638b8ce855fea1a60ccaf623c559f53c1408154d
Reviewed-on: https://chromium-review.googlesource.com/c/1314594
Commit-Queue: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605071}

android_webview/browser/aw_settings.cc

@@ -24,6 +24,7 @@
 #include "content/public/common/renderer_preferences.h"
 #include "content/public/common/web_preferences.h"
 #include "jni/AwSettings_jni.h"
+#include "net/http/http_util.h"
 #include "services/network/public/cpp/features.h"
 #include "ui/gfx/font_render_params.h"
 
@@ -256,7 +257,7 @@ void AwSettings::UpdateRendererPreferencesLocked(
     content::StoragePartition* storage_partition =
         content::BrowserContext::GetDefaultStoragePartition(aw_browser_context);
     storage_partition->GetNetworkContext()->SetAcceptLanguage(
-        prefs->accept_languages);
+        net::HttpUtil::ExpandLanguageList(prefs->accept_languages));
   }
 }