Fix alignment of single-line entity suggestions.

This addresses a side effect of crrev.com/c/1934836, that stretches all
children. Default gravity for linear layout positioned items always on
top.

Bug: 1030722
Change-Id: I1a981be06feb2126c04f36aa7306b64beb68de9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1950856Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Ender <ender@google.com>
Cr-Commit-Position: refs/heads/master@{#721568}

chrome/android/java/res/layout/omnibox_entity_suggestion.xml

@@ -4,9 +4,9 @@
     found in the LICENSE file. -->
 <LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
-    android:id="@+id/omnibox_answer"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
+    android:gravity="center"
     android:orientation="vertical"
     android:minHeight="@dimen/omnibox_suggestion_height"
     android:paddingVertical="10dp">