Enable spare RenderProcessHost to be preinitialized.

chrome/android/java/src/org/chromium/chrome/browser/WarmupManager.java

 // Copyright 2015 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.
 
 package org.chromium.chrome.browser;
 
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.net.Uri;
 import android.os.AsyncTask;
@@ skipping 237 matching lines @@
         if (mDnsRequestsInFlight.contains(url)) {
             // Note that if two requests come for the same URL with two different profiles, the last
             // one will win.
             mPendingPreconnectWithProfile.put(url, profile);
         } else {
             nativePreconnectUrlAndSubresources(profile, url);
         }
     }
 
     /**
+     * Warms up a spare, empty RenderProcessHost that may be used for subsequent navigations.
+     *
+     * The spare RenderProcessHost will be used automatically in subsequent navigations.
+     * There is nothing further the WarmupManager needs to do to enable that use.
+     *
+     * This uses a different mechanism than createSpareWebContents, below, and is subject
+     * to fewer restrictions.
+     *
+     * This must be called from the UI thread.
+     */
+    public void createSpareRenderProcessHost(Profile profile) {
+        ThreadUtils.assertOnUiThread();
+        if (ChromeFeatureList.isEnabled(ChromeFeatureList.OMNIBOX_SPARE_RENDERER)) {
+            // Spare WebContents should not be used with spare RenderProcessHosts, but if one
+            // has been created, destroy it in order not to consume too many processes.
+            destroySpareWebContents();
+            nativeWarmupSpareRenderer(profile);
+        }
+    }
+
+    /**
      * Creates and initializes a spare WebContents, to be used in a subsequent navigation.
      *
      * This creates a renderer that is suitable for any navigation. It can be picked up by any tab.
      * Can be called multiple times, and must be called from the UI thread.
      * Note that this is a no-op on low-end devices.
      */
     public void createSpareWebContents() {
         ThreadUtils.assertOnUiThread();
         if (mSpareWebContents != null || SysUtils.isLowEndDevice()) return;
         mSpareWebContents = WebContentsFactory.createWebContentsWithWarmRenderer(false, false);
@@ skipping 45 matching lines @@
         mSpareWebContents = null;
         mObserver = null;
     }
 
     private static void recordWebContentsStatus(int status) {
         RecordHistogram.recordEnumeratedHistogram(
                 WEBCONTENTS_STATUS_HISTOGRAM, status, WEBCONTENTS_STATUS_COUNT);
     }
 
     private static native void nativePreconnectUrlAndSubresources(Profile profile, String url);
+    private static native void nativeWarmupSpareRenderer(Profile profile);
 }