Inherit default text color from MainTheme.

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

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2016 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
 <LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:orientation="vertical"
     android:padding="@dimen/infobar_padding" >
 
     <TextView
         android:id="@+id/header_view"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:fontFamily="sans-serif-medium"
         android:text="@string/tab_switcher_callout_header"
-        android:textSize="@dimen/infobar_big_icon_message_size"
-        android:textColor="@color/default_text_color" />
+        android:textSize="@dimen/infobar_big_icon_message_size" />
 
     <TextView
         android:id="@+id/description_view"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginTop="8dp"
         android:text="@string/tab_switcher_callout_body"
         android:textSize="@dimen/infobar_descriptive_text_size"
         android:textColor="@color/descriptive_text_color" />
 
     <Button
         android:id="@+id/confirm_button"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginTop="24dp"
         android:layout_gravity="end"
         android:background="?android:attr/selectableItemBackground"
         android:paddingStart="16dp"
         android:paddingEnd="16dp"
         android:text="@string/ok_got_it"
         android:textColor="@color/infobar_accent_blue" />
 
 </LinearLayout>