Add LanguageSettingsAndroid in fieldtrial_testing_config.

To fix the warning from cl/184235490, we need to add the missing
Chromium field trial config.

Bug: 808935
Change-Id: I2624b09a27175a2d24f631ac77175dfc69c5ff1f
Reviewed-on: https://chromium-review.googlesource.com/901042Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Leo Zhang <googleo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534557}

testing/variations/fieldtrial_testing_config.json

@@ -342,6 +342,21 @@
             ]
         }
     ],
+    "AndroidLanguageSettings": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "LanguagesPreference"
+                    ]
+                }
+            ]
+        }
+    ],
     "AndroidSpellChecker": [
         {
             "platforms": [