[Autofill Assistant] Horizontally center text on Buttons.

Bug: 806868
Change-Id: I69bdb935ea8029e64fa05172762262e2167659ec
Reviewed-on: https://chromium-review.googlesource.com/c/1347280Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Mathias Carlen <mcarlen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611047}

chrome/android/java/res_autofill_assistant/layout/autofill_assistant_button_filled.xml

@@ -8,7 +8,7 @@
     android:layout_height="wrap_content"
     android:paddingStart="24dp"
     android:paddingEnd="24dp"
-    android:gravity="center_vertical"
+    android:gravity="center_vertical|center_horizontal"
     android:minHeight="36dp"
     android:singleLine="true"
     style="@style/FilledButton" />

chrome/android/java/res_autofill_assistant/layout/autofill_assistant_button_hairline.xml

@@ -8,7 +8,7 @@
     android:layout_height="wrap_content"
     android:paddingStart="24dp"
     android:paddingEnd="24dp"
-    android:gravity="center_vertical"
+    android:gravity="center_vertical|center_horizontal"
     android:minHeight="36dp"
     android:singleLine="true"
     style="@style/TextButton" />

chrome/android/java/res_autofill_assistant/layout/autofill_assistant_chip_assistive.xml

@@ -9,7 +9,7 @@
     android:paddingStart="16dp"
     android:paddingEnd="16dp"
     android:textAppearance="@style/BlackTitle2"
-    android:gravity="center_vertical"
+    android:gravity="center_vertical|center_horizontal"
     android:minHeight="32dp"
     android:singleLine="true"
     android:background="@drawable/autofill_assistant_chip_assistive_bg" />