[Merge 109] Fix reorder mode autoscroll for tab groups on strip

Fix reorder mode autoscroll for tab groups on strip.
-Restore auto-scroll upon entering reorder mode.
-Allocate additional space to auto-scroll when the tabs do not fill the
 tab strip.

Long tabstrip vid: https://drive.google.com/file/d/1tsqAx95D0xtj6TqPG8zKd2shTQb5Nk-B/view?usp=sharing
Short tabstrip vid: https://drive.google.com/file/d/1V2UcUMOKQlbFsUiy1cqUDP_-OT-zsGhU/view?usp=sharing

(cherry picked from commit 2358792)

Bug: 1374918, 1368742
Change-Id: I6acf7cdfe56987d824de107d1f75029f55b669f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4063359
Commit-Queue: Neil Coronado <nemco@google.com>
Reviewed-by: Sirisha Kavuluru <skavuluru@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1077748}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4080600
Cr-Commit-Position: refs/branch-heads/5414@{#497}
Cr-Branched-From: 4417ee5-refs/heads/main@{#1070088}

chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutHelper.java

@@ -184,6 +184,7 @@ public Float get(StripLayoutHelper object) {
     private float mLastReorderX;
     private float mTabMarginWidth;
     private float mStripStartMarginForReorder;
+    private float mReorderExtraMinScrollOffset;
     private long mLastReorderScrollTime;
     private long mLastUpdateTime;
     private long mHoverStartTime;
@@ -1278,7 +1279,7 @@ private void updateSpinners(long time) {
 
     private void updateScrollOffsetPosition(float pos) {
         float oldScrollOffset = mScrollOffset;
-        mScrollOffset = MathUtils.clamp(pos, mMinScrollOffset, 0);
+        mScrollOffset = MathUtils.clamp(pos, mMinScrollOffset - mReorderExtraMinScrollOffset, 0);
 
         if (mInReorderMode && mScroller.isFinished()) {
             float delta = MathUtils.flipSignIf(
@@ -1830,7 +1831,13 @@ private void autoScrollForTabGroupMargins(
         float startValue = mScrollOffset - startMarginDelta;
         float endValue = startValue - delta;
 
-        if (startValue < mMinScrollOffset) return;
+        // If the current tab width is at its max, this means there are not enough tabs to fill the
+        // visible area on the tab strip. In this case, there is not enough room to auto-scroll for
+        // tab group margins. Allocate additional space to account for this. See
+        // http://crbug.com/1374918 for additional details.
+        if (mCachedTabWidth == mMaxTabWidth) {
+            mReorderExtraMinScrollOffset = mStripStartMarginForReorder + Math.abs(delta);
+        }
 
         if (animationList != null) {
             CompositorAnimator scrollAnimator =
@@ -1842,7 +1849,7 @@ private void autoScrollForTabGroupMargins(
         }
     }
 
-    private AnimatorListener getTabGroupMarginAnimatorListener() {
+    private AnimatorListener getTabGroupMarginAnimatorListener(boolean resetExtraMinScrollOffset) {
         return new AnimatorListenerAdapter() {
             @Override
             public void onAnimationStart(Animator animation) {
@@ -1852,6 +1859,7 @@ public void onAnimationStart(Animator animation) {
             @Override
             public void onAnimationEnd(Animator animation) {
                 mTabGroupMarginAnimRunning = false;
+                if (resetExtraMinScrollOffset) mReorderExtraMinScrollOffset = 0.f;
             }
         };
     }
@@ -1905,7 +1913,7 @@ private void computeAndUpdateTabGroupMargins(boolean autoScroll, boolean animate
 
         // 4. Begin slide-out and scroll animation. Update tab positions.
         if (animationList != null) {
-            startAnimationList(animationList, getTabGroupMarginAnimatorListener());
+            startAnimationList(animationList, getTabGroupMarginAnimatorListener(false));
         } else {
             computeTabInitialPositions();
         }
@@ -1934,7 +1942,7 @@ private void resetTabGroupMargins() {
         mStripStartMarginForReorder = 0f;
 
         // 3. Begin slide-out and scroll animation.
-        startAnimationList(animationList, getTabGroupMarginAnimatorListener());
+        startAnimationList(animationList, getTabGroupMarginAnimatorListener(true));
     }
 
     private void setCompositorButtonsVisible(boolean visible) {
@@ -2583,6 +2591,14 @@ float getMinimumScrollOffset() {
         return mMinScrollOffset;
     }
 
+    /**
+     * @return The strip's additional minimum scroll offset for reorder mode.
+     */
+    @VisibleForTesting
+    float getReorderExtraMinScrollOffset() {
+        return mReorderExtraMinScrollOffset;
+    }
+
     /**
      * @return The scroller.
      */

chrome/android/junit/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutHelperTest.java

@@ -1399,6 +1399,37 @@ public void testReorder_MergeToGroup() {
                 .mergeTabsToGroup(eq(thirdTab.getId()), eq(oldSecondTabId), eq(true));
     }
 
+    @Test
+    @Feature("Tab Groups on Tab Strip")
+    public void testReorder_NoExtraMinScroll() {
+        // Mock 3 tabs. Group the first two tabs.
+        initializeTest(false, false, true, 0, 3);
+        mStripLayoutHelper.onSizeChanged(SCREEN_WIDTH, SCREEN_HEIGHT, false, TIMESTAMP);
+
+        // Start reorder mode on third tab.
+        mStripLayoutHelper.startReorderModeAtIndexForTesting(2);
+
+        // Verify extra scroll offset.
+        assertEquals("Extra min offset should not be set.", 0f,
+                mStripLayoutHelper.getReorderExtraMinScrollOffset(), EPSILON);
+    }
+
+    @Test
+    @Feature("Tab Groups on Tab Strip")
+    public void testReorder_ExtraMinScroll() {
+        // Mock 3 tabs. Group the first two tabs.
+        initializeTest(false, false, true, 0, 3);
+        mStripLayoutHelper.onSizeChanged(SCREEN_WIDTH, SCREEN_HEIGHT, false, TIMESTAMP);
+        groupTabs(0, 2);
+
+        // Start reorder mode on third tab.
+        mStripLayoutHelper.startReorderModeAtIndexForTesting(2);
+
+        // Verify extra scroll offset.
+        assertNotEquals("Extra min offset should be set.", 0f,
+                mStripLayoutHelper.getReorderExtraMinScrollOffset(), EPSILON);
+    }
+
     @Test
     @Feature("Tab Strip Improvements")
     public void testTabClosing_NoTabResize() {