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

This reverts commit 5c5957c7.

Reason for revert: testMergeOnMultiDisplay_OnDisplayChanged failing on test-n-phone
https://ci.chromium.org/p/chrome/builders/ci/test-n-phone

Original change's description:
> Merge tabs of multi-instance when display is changed.
> 
> On partner foldable phones, when the secondary display is off, there
> is only one targetable displays and only #onDisplayChanged is called.
> This CL tries to merge tabs #onDisplayChanged as well.
> 
> Bug: 1088202
> Change-Id: Id21960b40bceb4b04fce7a2718c0e33bee0f4920
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2272131
> Reviewed-by: Theresa  <twellington@chromium.org>
> Commit-Queue: Lijin Shen <lazzzis@google.com>
> Cr-Commit-Position: refs/heads/master@{#786055}

TBR=tedchoc@chromium.org,twellington@chromium.org,lazzzis@google.com

Change-Id: I73c428b30eb6005f4e85171434dec16d54d4e419
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1088202
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288809Reviewed-by: Lijin Shen <lazzzis@google.com>
Reviewed-by: Natalie Chouinard <chouinard@chromium.org>
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786487}

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

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

@@ -55,7 +55,6 @@ import org.chromium.content_public.browser.test.util.CriteriaHelper;
 import org.chromium.content_public.browser.test.util.TestThreadUtils;
 import org.chromium.ui.test.util.UiRestriction;
 
-import java.util.Collections;
 import java.util.concurrent.TimeoutException;
 
 /**
@@ -540,45 +539,4 @@ public class TabModelMergingTest {
         mActivity1.finishAndRemoveTask();
         mActivity2.finishAndRemoveTask();
     }
-
-    @Test
-    @LargeTest
-    @EnableFeatures(ChromeFeatureList.ANDROID_MULTIPLE_DISPLAY)
-    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();
-    }
 }