Cancel keydown events immediately once the view starts scrolling

The motivation of this patch is to make sure a user never feel
haptic feedback when scrolling the Emoji palette. In order to
achieve it, EmojiPageKeyboardView#releaseCurrentKey() should
be called whenever (delayed) keydown events should be canceled.

This patch wires up ViewPager.OnPageChangeListener#onPageScrolled
with EmojiPageKeyboardView#releaseCurrentKey() so that delayed
keydown events will be canceled immediately once the ViewParger
starts scrolling.

BUG: 12964092
Change-Id: Iea8c3e090bb16a8622e6b4a850af2bf963aa77d0

java/src/com/android/inputmethod/keyboard/EmojiPalettesView.java

@@ -534,6 +534,7 @@ public final class EmojiPalettesView extends LinearLayout implements OnTabChange
     @Override
     public void onPageScrolled(final int position, final float positionOffset,
             final int positionOffsetPixels) {
+        mEmojiPalettesAdapter.onPageScrolled();
         final Pair<Integer, Integer> newPos =
                 mEmojiCategory.getCategoryIdAndPageIdFromPagePosition(position);
         final int newCategoryId = newPos.first;
@@ -718,6 +719,14 @@ public final class EmojiPalettesView extends LinearLayout implements OnTabChange
             }
         }
 
+        public void onPageScrolled() {
+            // Make sure the delayed key-down event (highlight effect and haptic feedback) will be
+            // canceled.
+            final EmojiPageKeyboardView currentKeyboardView =
+                  mActiveKeyboardViews.get(mActivePosition);
+            currentKeyboardView.releaseCurrentKey();
+        }
+
         @Override
         public int getCount() {
             return mEmojiCategory.getTotalPageCountOfAllCategories();