Reenable TabModelMergingTest on Pie

Add FLAG_ACTIVITY_NEW_TASK to intents used to launch new
activities in TabModelMergintTest, and reenable
 #testMergeOnColdStartIntoChromeTabbedActivity2 on Pie.

BUG=1036551

Change-Id: I995f1f4e5aeeb0c533e55fc9b8000e534613e9aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120748
Auto-Submit: Theresa  <twellington@chromium.org>
Commit-Queue: Ted Choc <tedchoc@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753338}

chrome/android/javatests/src/org/chromium/chrome/browser/tabmodel/TabModelMergingTest.java

@@ -394,6 +394,7 @@ public class TabModelMergingTest {
         // Send a main intent to restart ChromeTabbedActivity2.
         Intent CTA2MainIntent = new Intent(Intent.ACTION_MAIN);
         CTA2MainIntent.setClassName(CTA2PackageName, CTA2ClassName);
+        CTA2MainIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
         InstrumentationRegistry.getInstrumentation().startActivitySync(CTA2MainIntent);
 
         mNewCTA2CallbackHelper.waitForCallback(0);

testing/buildbot/filters/android.emulator.chrome_public_test_apk.filter

@@ -21,9 +21,6 @@
 # crbug/1032118
 -org.chromium.chrome.browser.notifications.StandardNotificationBuilderTest.testSetAll
 
-# crbug/1036551
--org.chromium.chrome.browser.tabmodel.TabModelMergingTest.testMergeOnColdStartIntoChromeTabbedActivity2
-
 # crbug/1036459
 -org.chromium.chrome.browser.ntp.NewTabPageTest.testFocusFakebox
 

testing/buildbot/filters/android.pie_arm64_rel.chrome_public_test_apk.filter

@@ -40,9 +40,6 @@
 -org.chromium.chrome.browser.suggestions.tile.TileGroupTest.testDismissTileUndo
 -org.chromium.chrome.browser.suggestions.tile.TileGroupTest.testDismissTileWithContextMenu
 
-# crbug/1036551
--org.chromium.chrome.browser.tabmodel.TabModelMergingTest.testMergeOnColdStartIntoChromeTabbedActivity2
-
 # crbug/1017141
 -org.chromium.chrome.browser.tasks.tab_management.TabSwitcherMultiWindowTest.testMoveTabsAcrossWindow_GTS_WithoutGroup