📰 Stop refreshing the whole NTP for every adapter change

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java
index 63482506e42039b7365ad72cc92c74231d399186..7c8f5dcba3f59f51c5f6be1cb51e70efe43b9476 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SuggestionsSection.java
@@ -28,11 +28,24 @@
     private final ActionItem mMoreButton;
     @CategoryInt
     private final int mCategory;
+    private final Observer mObserver;
 
     public SuggestionsSection(@CategoryInt int category, SuggestionsCategoryInfo info,
             final NewTabPageAdapter adapter) {
+        this(category, info, adapter, new ActionDelegate() {
+            @Override
+            public void onButtonTapped() {
+                adapter.reloadSnippets();
+            }
+        });
+    }
+
+    @VisibleForTesting
+    SuggestionsSection(@CategoryInt int category, SuggestionsCategoryInfo info, Observer observer,
+            ActionDelegate actionDelegate) {
         mHeader = new SectionHeader(info.getTitle());
         mCategory = category;
+        mObserver = observer;
 
         // TODO(dgn): Properly define strings, actions, etc. for each section and category type.
         if (info.hasMoreButton()) {
@@ -40,12 +53,7 @@ public SuggestionsSection(@CategoryInt int category, SuggestionsCategoryInfo inf
             mActionDelegate = null;
         } else {
             mMoreButton = null;
-            mActionDelegate = new ActionDelegate() {
-                @Override
-                public void onButtonTapped() {
-                    adapter.reloadSnippets();
-                }
-            };
+            mActionDelegate = actionDelegate;
         }
     }
 
@@ -63,8 +71,20 @@ public void onButtonTapped() {
     }
 
     public void removeSuggestion(SnippetArticle suggestion) {
-        mSuggestions.remove(suggestion);
+        int removedIndex = mSuggestions.indexOf(suggestion);
+        if (removedIndex == -1) return;
+        mSuggestions.remove(removedIndex);
         if (mMoreButton != null) mMoreButton.setDismissable(!hasSuggestions());
+        if (hasSuggestions()) {
+            mObserver.notifyItemRemoved(
+                    this, removedIndex + 1 /* Header has index 0 in the section */);
+        } else {
+            int itemCountAfter = getItems().size();
+            // When we remove the last suggestion, we add 2 items: status card and progress
+            // indicator, so the count after has one more item than the count before.
+            int itemCountBefore = itemCountAfter - 1;
+            mObserver.notifyGroupChanged(this, itemCountBefore, itemCountAfter);
+        }
     }
 
     public void removeSuggestionById(String suggestionId) {
@@ -87,7 +107,8 @@ public int getSuggestionsCount() {
     public void setSuggestions(List<SnippetArticle> suggestions, @CategoryStatusEnum int status) {
         copyThumbnails(suggestions);
 
-        setStatus(status);
+        int itemCountBefore = getItems().size();
+        setStatusInternal(status);
 
         mSuggestions.clear();
         mSuggestions.addAll(suggestions);
@@ -95,10 +116,17 @@ public void setSuggestions(List<SnippetArticle> suggestions, @CategoryStatusEnum
         if (mMoreButton != null) {
             mMoreButton.setPosition(mSuggestions.size());
         }
+        mObserver.notifyGroupChanged(this, itemCountBefore, getItems().size());
     }
 
     /** Sets the status for the section. Some statuses can cause the suggestions to be cleared. */
     public void setStatus(@CategoryStatusEnum int status) {
+        int itemCountBefore = getItems().size();
+        setStatusInternal(status);
+        mObserver.notifyGroupChanged(this, itemCountBefore, getItems().size());
+    }
+
+    private void setStatusInternal(@CategoryStatusEnum int status) {
         mStatus = StatusItem.create(status, mActionDelegate);
 
         if (!SnippetsBridge.isCategoryStatusAvailable(status)) mSuggestions.clear();