Use a delayed post task for Omnibox Spare Renderer on Android

We'll experiment with the delay to find something ideal.

Bug: 730587
Change-Id: Ib583939abfbf641f43ce15103ce20e75a9fae4e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412551Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807539}

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

@@ -27,7 +27,6 @@ import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.task.AsyncTask;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.app.ChromeActivity;
-import org.chromium.chrome.browser.flags.ChromeFeatureList;
 import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.chrome.browser.toolbar.ControlContainer;
 import org.chromium.components.embedder_support.util.UrlConstants;
@@ -333,12 +332,9 @@ public class WarmupManager {
     public void createSpareRenderProcessHost(Profile profile) {
         ThreadUtils.assertOnUiThread();
         if (!LibraryLoader.getInstance().isInitialized()) return;
-        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();
-            WarmupManagerJni.get().warmupSpareRenderer(profile);
-        }
+
+        destroySpareWebContents();
+        WarmupManagerJni.get().warmupSpareRenderer(profile);
     }
 
     /**

chrome/android/java/src/org/chromium/chrome/browser/omnibox/suggestions/AutocompleteController.java

@@ -13,9 +13,12 @@ import androidx.annotation.VisibleForTesting;
 import androidx.collection.ArraySet;
 
 import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.NativeMethods;
+import org.chromium.base.task.PostTask;
 import org.chromium.chrome.browser.WarmupManager;
+import org.chromium.chrome.browser.flags.ChromeFeatureList;
 import org.chromium.chrome.browser.ntp.NewTabPage;
 import org.chromium.chrome.browser.omnibox.OmniboxSuggestionType;
 import org.chromium.chrome.browser.omnibox.suggestions.AutocompleteResult.GroupDetails;
@@ -25,6 +28,7 @@ import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.components.omnibox.SuggestionAnswer;
 import org.chromium.components.query_tiles.QueryTile;
+import org.chromium.content_public.browser.UiThreadTaskTraits;
 import org.chromium.content_public.browser.WebContents;
 import org.chromium.url.GURL;
 
@@ -168,10 +172,23 @@ public class AutocompleteController {
         assert mListener != null : "Ensure a listener is set prior to calling.";
         if (profile == null || TextUtils.isEmpty(url)) return;
 
-        if (!NewTabPage.isNTPUrl(url)) {
-            // Proactively start up a renderer, to reduce the time to display search results,
-            // especially if a Service Worker is used.
-            WarmupManager.getInstance().createSpareRenderProcessHost(profile);
+        // Proactively start up a renderer, to reduce the time to display search results,
+        // especially if a Service Worker is used. This is done in a PostTask with a
+        // experiment-configured delay so that the CPU usage associated with starting a new renderer
+        // process does not impact the Omnibox initialization. Note that there's a small chance the
+        // renderer will be started after the next navigation if the delay is too long, but the
+        // spare renderer will probably get used anyways by a later navigation.
+        if (!NewTabPage.isNTPUrl(url)
+                && ChromeFeatureList.isEnabled(ChromeFeatureList.OMNIBOX_SPARE_RENDERER)) {
+            PostTask.postDelayedTask(UiThreadTaskTraits.BEST_EFFORT,
+                    ()
+                            -> {
+                        ThreadUtils.assertOnUiThread();
+                        WarmupManager.getInstance().createSpareRenderProcessHost(profile);
+                    },
+                    ChromeFeatureList.getFieldTrialParamByFeatureAsInt(
+                            ChromeFeatureList.OMNIBOX_SPARE_RENDERER,
+                            "omnibox_spare_renderer_delay_ms", 0));
         }
         mNativeAutocompleteControllerAndroid =
                 AutocompleteControllerJni.get().init(AutocompleteController.this, profile);