customtabs: Re-Create a spare renderer on Tab close.

In a lot of cases, several Custom Tabs are created in a sequence,
without the embedding application calling warmup() in between
launches. This means that spare renderer is only available the first
time.

This changes re-creates a spare renderer once the Custom Tab is closed.

BUG=617214

Review-Url: https://chromiumcodereview.appspot.com/2431833002
Cr-Commit-Position: refs/heads/master@{#426552}

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java

@@ -157,7 +157,7 @@ public class CustomTabActivity extends ChromeActivity {
         public void didCloseTab(int tabId, boolean incognito) {
             PageLoadMetrics.removeObserver(mMetricsObserver);
             // Finish the activity after we intent out.
-            if (getTabModelSelector().getCurrentModel().getCount() == 0) finish();
+            if (getTabModelSelector().getCurrentModel().getCount() == 0) finishAndClose(false);
         }
     };
 
@@ -363,7 +363,7 @@ public class CustomTabActivity extends ChromeActivity {
                     @Override
                     public void onClick(View v) {
                         RecordUserAction.record("CustomTabs.CloseButtonClicked");
-                        finishAndClose();
+                        finishAndClose(false);
                     }
                 });
 
@@ -644,9 +644,25 @@ public class CustomTabActivity extends ChromeActivity {
 
     /**
      * Finishes the activity and removes the reference from the Android recents.
+     *
+     * @param reparenting true iff the activity finishes due to tab reparenting.
      */
-    public final void finishAndClose() {
+    public final void finishAndClose(boolean reparenting) {
         mIsClosing = true;
+        if (!reparenting) {
+            // Closing the activity destroys the renderer as well. Re-create a spare renderer some
+            // time after, so that we have one ready for the next tab open. This does not increase
+            // memory consumption, as the current renderer goes away. We create a renderer as a lot
+            // of users open several Custom Tabs in a row. The delay is there to avoid jank in the
+            // transition animation when closing the tab.
+            ThreadUtils.postOnUiThreadDelayed(new Runnable() {
+                @Override
+                public void run() {
+                    WarmupManager.getInstance().createSpareWebContents();
+                }
+            }, 500);
+        }
+
         handleFinishAndClose();
     }
 
@@ -671,7 +687,7 @@ public class CustomTabActivity extends ChromeActivity {
             if (getCurrentTabModel().getCount() > 1) {
                 getCurrentTabModel().closeTab(getActivityTab(), false, false, false);
             } else {
-                finishAndClose();
+                finishAndClose(false);
             }
         }
         return true;
@@ -823,7 +839,7 @@ public class CustomTabActivity extends ChromeActivity {
             Runnable finalizeCallback = new Runnable() {
                 @Override
                 public void run() {
-                    finishAndClose();
+                    finishAndClose(true);
                 }
             };
 

chrome/android/javatests/src/org/chromium/chrome/browser/customtabs/CustomTabActivityTest.java

@@ -54,6 +54,7 @@ import org.chromium.chrome.browser.ChromeSwitches;
 import org.chromium.chrome.browser.ChromeTabbedActivity;
 import org.chromium.chrome.browser.IntentHandler;
 import org.chromium.chrome.browser.TabsOpenedFromExternalAppTest;
+import org.chromium.chrome.browser.WarmupManager;
 import org.chromium.chrome.browser.appmenu.AppMenuHandler;
 import org.chromium.chrome.browser.document.ChromeLauncherActivity;
 import org.chromium.chrome.browser.metrics.PageLoadMetrics;
@@ -1146,6 +1147,35 @@ public class CustomTabActivityTest extends CustomTabActivityTestBase {
         });
     }
 
+    @SmallTest
+    @Restriction(RESTRICTION_TYPE_NON_LOW_END_DEVICE)
+    public void testRecreateSpareRendererOnTabClose() throws Exception {
+        Context context = getInstrumentation().getTargetContext().getApplicationContext();
+        warmUpAndWait();
+
+        try {
+            startCustomTabActivityWithIntent(
+                    CustomTabsTestUtils.createMinimalCustomTabIntent(context, mTestPage));
+        } catch (InterruptedException e) {
+            fail();
+        }
+
+        ThreadUtils.runOnUiThreadBlocking(new Runnable() {
+            @Override
+            public void run() {
+                assertFalse(WarmupManager.getInstance().hasSpareWebContents());
+                final CustomTabActivity activity = (CustomTabActivity) getActivity();
+                activity.finishAndClose(false);
+            }
+        });
+        CriteriaHelper.pollUiThread(new Criteria("No new spare renderer") {
+            @Override
+            public boolean isSatisfied() {
+                return WarmupManager.getInstance().hasSpareWebContents();
+            }
+        }, 2000, 200);
+    }
+
     /**
      * Tests that prerendering accepts a referrer, and that this is not lost when launching the
      * Custom Tab.