[Unity][Android] Fix margins in signin_view

This CL updates margins in signin_view.xml to match the mocks.

Bug: 927425
Change-Id: Ibe93a7768a041f8d93fe2d802e1097d2e4d3b81f
Reviewed-on: https://chromium-review.googlesource.com/c/1456059
Auto-Submit: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629775}

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

@@ -105,7 +105,7 @@
                 android:layout_height="wrap_content"
                 android:layout_below="@id/signin_account_picker"
                 android:layout_marginStart="16dp"
-                android:layout_marginTop="28dp"
+                android:layout_marginTop="16dp"
                 android:layout_marginEnd="16dp"
                 android:textAppearance="@style/TextAppearance.BlackTitle1"
                 tools:text="@string/signin_sync_title"/>
@@ -123,7 +123,7 @@
                 style="@style/HorizontalDivider"
                 android:layout_below="@id/signin_sync_description"
                 android:layout_marginStart="16dp"
-                android:layout_marginTop="12dp"
+                android:layout_marginTop="16dp"
                 android:layout_marginEnd="16dp"/>
             <TextView
                 android:id="@+id/signin_details_description"