Custom Tabs: use spare web contents when initially hidden.

This is necessary for the background tab to use the spare web contents.

Bug: 821397
Change-Id: I9f140134179d258e012ca749d28c109fee671320
Reviewed-on: https://chromium-review.googlesource.com/960903
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543114}

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

@@ -287,7 +287,8 @@ public final class WarmupManager {
         ThreadUtils.assertOnUiThread();
         if (!LibraryLoader.isInitialized()) return;
         if (mSpareWebContents != null || SysUtils.isLowEndDevice()) return;
-        mSpareWebContents = WebContentsFactory.createWebContentsWithWarmRenderer(false, false);
+        mSpareWebContents = WebContentsFactory.createWebContentsWithWarmRenderer(
+                false /* incognito */, true /* initiallyHidden */);
         mObserver = new RenderProcessGoneObserver();
         mSpareWebContents.addObserver(mObserver);
         mWebContentsCreationTimeMs = SystemClock.elapsedRealtime();
@@ -313,12 +314,13 @@ public final class WarmupManager {
      */
     public WebContents takeSpareWebContents(boolean incognito, boolean initiallyHidden) {
         ThreadUtils.assertOnUiThread();
-        if (incognito || initiallyHidden) return null;
+        if (incognito) return null;
         WebContents result = mSpareWebContents;
         if (result == null) return null;
         mSpareWebContents = null;
         result.removeObserver(mObserver);
         mObserver = null;
+        if (!initiallyHidden) result.onShow();
         recordWebContentsStatus(WEBCONTENTS_STATUS_USED);
         return result;
     }

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

@@ -1378,6 +1378,7 @@ public class CustomTabsConnection {
             case SpeculationParams.HIDDEN_TAB:
                 recordSpeculationStatusOnStart(SPECULATION_STATUS_ON_START_BACKGROUND_TAB);
                 launchUrlInHiddenTab(session, url, extras);
+                createSpareWebContents = false;
                 break;
             default:
                 break;

chrome/android/javatests/src/org/chromium/chrome/browser/WarmupManagerTest.java

@@ -134,9 +134,10 @@ public class WarmupManagerTest {
     public void testTakeSpareWebContentsChecksArguments() throws Throwable {
         mWarmupManager.createSpareWebContents();
         Assert.assertNull(mWarmupManager.takeSpareWebContents(true, false));
-        Assert.assertNull(mWarmupManager.takeSpareWebContents(false, true));
         Assert.assertNull(mWarmupManager.takeSpareWebContents(true, true));
         Assert.assertTrue(mWarmupManager.hasSpareWebContents());
+        Assert.assertNotNull(mWarmupManager.takeSpareWebContents(false, true));
+        Assert.assertFalse(mWarmupManager.hasSpareWebContents());
     }
 
     @Test