NTP: fix bad layout when navigating back from a page with a theme-color.

chrome/android/java/res/layout/new_tab_page_layout.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. -->
 <org.chromium.chrome.browser.ntp.NewTabPageLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:chrome="http://schemas.android.com/apk/res-auto"
     android:id="@+id/ntp_content"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:layout_gravity="center_horizontal"
     android:orientation="vertical"
     android:gravity="center"
     android:paddingTop="@dimen/toolbar_height_no_shadow"
     android:visibility="gone" >
 
-    <!-- Spacer. Note: this must have layout_weight="1" and the other spacers must have
-         layout_weight="0". The NewTabPageLayout will redistribute the extra space between
-         them. -->
+    <!-- Top spacer. Note: the top spacer must have layout_weight="1" and the middle and bottom
+         spacers must have layout_weight="0". The NewTabPageLayout will redistribute the extra space
+         between them. -->
     <View
         android:id="@+id/ntp_top_spacer"
         android:layout_width="0dp"
         android:layout_height="0dp"
         android:layout_weight="1"
         android:visibility="invisible" />
 
     <!-- Search provider logo -->
     <org.chromium.chrome.browser.ntp.LogoView
         android:id="@+id/search_provider_logo"
@@ skipping 33 matching lines @@
         <org.chromium.chrome.browser.widget.TintedImageView
             android:id="@+id/voice_search_button"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_marginStart="12dp"
             android:layout_marginEnd="12dp"
             android:contentDescription="@string/accessibility_toolbar_btn_mic"
             android:src="@drawable/btn_mic" />
     </LinearLayout>
 
-    <!-- Spacer -->
+    <!-- Middle spacer -->
     <View
         android:id="@+id/ntp_middle_spacer"
         android:layout_width="0dp"
         android:layout_height="0dp"
         android:layout_weight="0"
         android:visibility="invisible" />
 
     <!-- Most visited items -->
     <org.chromium.chrome.browser.ntp.MostVisitedLayout
         android:id="@+id/most_visited_layout"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginBottom="16dp"
         android:layout_marginStart="12dp"
         android:layout_marginEnd="12dp"
         android:layout_gravity="center_horizontal"
         android:paddingTop="@dimen/most_visited_layout_padding_top"
         android:paddingBottom="4dp" />
 
     <!-- Most visited items placeholder -->
     <ViewStub
         android:id="@+id/most_visited_placeholder_stub"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_weight="1"
         android:inflatedId="@+id/most_visited_placeholder"
         android:layout="@layout/most_visited_placeholder" />
 
-    <!-- Spacer -->
+    <!-- Bottom spacer -->
     <View
         android:id="@+id/ntp_bottom_spacer"
         android:layout_width="0dp"
         android:layout_height="0dp"
         android:layout_weight="0"
         android:visibility="invisible" />
 
+    <!--  Logo spacer -->
     <View
         android:id="@+id/no_search_logo_spacer"
         android:layout_width="match_parent"
         android:layout_height="0dp"
         android:layout_weight="1"
         android:visibility="gone" />
 
+    <!--  Scroll spacer -->
     <View
         android:id="@+id/ntp_scroll_spacer"
         android:layout_width="match_parent"
         android:layout_height="0dp"
         android:visibility="gone" />
 </org.chromium.chrome.browser.ntp.NewTabPageLayout>