Fix up a few more lint warnings in chrome/

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

Index: chrome/android/java/res/layout/autofill_card_unmask_prompt.xml
diff --git a/chrome/android/java/res/layout/autofill_card_unmask_prompt.xml b/chrome/android/java/res/layout/autofill_card_unmask_prompt.xml
index feabdf1998604c6222220f3367106301e002847c..69dddf9fd5df12274161a98f3c8fb1138322f75c 100644
--- a/chrome/android/java/res/layout/autofill_card_unmask_prompt.xml
+++ b/chrome/android/java/res/layout/autofill_card_unmask_prompt.xml
@@ -82,7 +82,8 @@
                 android:layout_height="wrap_content"
                 android:layout_gravity="center_vertical"
                 android:layout_marginStart="8dp"
-                android:layout_marginEnd="16dp" />
+                android:layout_marginEnd="16dp"
+                android:contentDescription="@null" />
         </LinearLayout>
 
         <TextView
@@ -126,12 +127,14 @@
             android:layout_marginTop="30dp"
             android:visibility="gone" />
 
+        <!--  TODO(estade): add a real content description for this image. -->
         <ImageView
             android:id="@+id/verification_success"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:src="@drawable/verify_checkmark"
-            android:visibility="gone" />
+            android:visibility="gone"
+            android:contentDescription="@null" />
 
         <TextView
             android:id="@+id/verification_message"