Reland "Merge tabs of multi-instance when display is changed."

Reland https://crrev.com/c/2272131

1. Enable only on P+
2. Use new Critical Helper API

Bug: 1088202
Change-Id: I9d07ceee98d138a6468c6280266a14aea8e20b8b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2290961Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Lijin Shen <lazzzis@google.com>
Cr-Commit-Position: refs/heads/master@{#787925}

chrome/android/java/src/org/chromium/chrome/browser/multiwindow/MultiInstanceManager.java

@@ -20,6 +20,7 @@ import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 
 import org.chromium.base.ActivityState;
+import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.ApplicationStatus;
 import org.chromium.base.CommandLine;
 import org.chromium.base.metrics.RecordUserAction;
@@ -85,6 +86,7 @@ public class MultiInstanceManager
     private boolean mShouldMergeOnConfigurationChange;
     private boolean mIsRecreating;
     private int mDisplayId;
+    private static List<Integer> sTestDisplayIds;
 
     /**
      * Create a new {@link MultiInstanceManager}.
@@ -220,7 +222,13 @@ public class MultiInstanceManager
 
             @Override
             public void onDisplayChanged(int displayId) {
-                // TODO(crbug.com/824954): try to merge tabs sharing logic w/ onDisplayRemoved
+                if (displayId == mDisplayId) return;
+                List<Integer> ids = sTestDisplayIds != null
+                    ? sTestDisplayIds
+                    : ApiCompatibilityUtils.getTargetableDisplayIds(mActivity);
+                if (ids.size() == 1 && ids.get(0).equals(mDisplayId)) {
+                    maybeMergeTabs();
+                }
             }
         };
         displayManager.registerDisplayListener(mDisplayListener, null);
@@ -433,4 +441,9 @@ public class MultiInstanceManager
     public DisplayManager.DisplayListener getDisplayListenerForTesting() {
         return mDisplayListener;
     }
+
+    @VisibleForTesting
+    public static void setTestDisplayIds(List<Integer> testDisplayIds) {
+        sTestDisplayIds = testDisplayIds;
+    }
 }

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

@@ -16,6 +16,7 @@ import android.support.test.InstrumentationRegistry;
 
 import androidx.test.filters.LargeTest;
 
+import java.util.Collections;
 import org.hamcrest.Matchers;
 import org.junit.Assert;
 import org.junit.Before;
@@ -539,4 +540,48 @@ public class TabModelMergingTest {
         mActivity1.finishAndRemoveTask();
         mActivity2.finishAndRemoveTask();
     }
+
+    @Test
+    @LargeTest
+    @EnableFeatures(ChromeFeatureList.ANDROID_MULTIPLE_DISPLAY)
+    @DisableIf.Build(sdk_is_less_than = VERSION_CODES.P)
+    public void testMergeOnMultiDisplay_OnDisplayChanged() throws TimeoutException {
+        TestThreadUtils.runOnUiThreadBlocking(() -> {
+            mActivity1.saveState();
+            mActivity2.saveState();
+        });
+        MultiInstanceManager m1 = mActivity1.getMultiInstanceMangerForTesting();
+        MultiInstanceManager m2 = mActivity2.getMultiInstanceMangerForTesting();
+
+        // Ensure Activity 1 is resumed on the front.
+        Intent intent = new Intent(mActivity1, mActivity1.getClass());
+        intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
+        mActivity1.startActivity(intent);
+        waitForActivityStateChange(ActivityState.RESUMED, mActivity2, false);
+        waitForActivityStateChange(ActivityState.RESUMED, mActivity1, true);
+
+        MultiInstanceManager.setTestDisplayIds(Collections.singletonList(0));
+        m1.setCurrentDisplayIdForTesting(0);
+        m2.setCurrentDisplayIdForTesting(1);
+
+        TestThreadUtils.runOnUiThreadBlocking(() -> {
+            m1.getDisplayListenerForTesting().onDisplayChanged(1);
+            m2.getDisplayListenerForTesting().onDisplayChanged(1);
+        });
+
+        CriteriaHelper.pollUiThread(() -> {
+            Criteria.checkThat("Total tab count incorrect.",
+                mActivity1.getTabModelSelector().getTotalTabCount(), Matchers.is(7));
+        });
+
+        CriteriaHelper.pollUiThread(() -> {
+            Criteria.checkThat("CTA should not be destroyed", mActivity1State,
+                Matchers.not(ActivityState.DESTROYED));
+            Criteria.checkThat("CTA2 should be destroyed", mActivity2State,
+                Matchers.is(ActivityState.DESTROYED));
+        });
+
+        mActivity1.finishAndRemoveTask();
+        mActivity2.finishAndRemoveTask();
+    }
 }