[Chromecast] Break dependency of Controller on ObserverList.

The special properties of ObserverList were not needed because
of how Controller uses a Sequencer to avoid concurrent
modification. This also avoids heap allocation of iterators and
the use of the O(n) memory Itertools.reverse() when closing
scopes.

Bug: None
Test: cast_base_junit_tests
Change-Id: I91ef516caf07de8b9a899c17b015f2e2838fee35
Reviewed-on: https://chromium-review.googlesource.com/1191087Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586378}

chromecast/base/java/src/org/chromium/chromecast/base/Controller.java

@@ -4,10 +4,10 @@
 
 package org.chromium.chromecast.base;
 
-import org.chromium.base.ObserverList;
-
 import java.util.ArrayDeque;
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 /**
@@ -21,19 +21,19 @@ import java.util.Map;
  */
 public class Controller<T> extends Observable<T> {
     private final Sequencer mSequencer = new Sequencer();
-    private final ObserverList<Observer<? super T>> mEnterObservers = new ObserverList<>();
+    private final List<Observer<? super T>> mObservers = new ArrayList<>();
     private final Map<Observer<? super T>, Scope> mScopeMap = new HashMap<>();
     private T mData = null;
 
     @Override
     public Scope watch(Observer<? super T> observer) {
         mSequencer.sequence(() -> {
-            mEnterObservers.addObserver(observer);
+            mObservers.add(observer);
             if (mData != null) notifyEnter(observer);
         });
         return () -> mSequencer.sequence(() -> {
             if (mData != null) notifyExit(observer);
-            mEnterObservers.removeObserver(observer);
+            mObservers.remove(observer);
         });
     }
 
@@ -65,8 +65,8 @@ public class Controller<T> extends Observable<T> {
             }
 
             mData = data;
-            for (Observer<? super T> observer : mEnterObservers) {
-                notifyEnter(observer);
+            for (int i = 0; i < mObservers.size(); i++) {
+                notifyEnter(mObservers.get(i));
             }
         });
     }
@@ -88,8 +88,8 @@ public class Controller<T> extends Observable<T> {
         assert mSequencer.inSequence();
         if (mData == null) return;
         mData = null;
-        for (Observer<? super T> observer : Itertools.reverse(mEnterObservers)) {
-            notifyExit(observer);
+        for (int i = mObservers.size() - 1; i >= 0; i--) {
+            notifyExit(mObservers.get(i));
         }
     }
 

chromecast/base/java/src/org/chromium/chromecast/base/Itertools.java

@@ -5,48 +5,11 @@
 package org.chromium.chromecast.base;
 
 import java.util.Iterator;
-import java.util.Stack;
 
 /**
  * Utility methods for working with Iterables and Iterators.
  */
 public class Itertools {
-    /**
-     * Iterate the given Iterable in reverse.
-     *
-     * This is inefficient, as the entire given Iterable needs to be iterated before the result can
-     * be iterated, and O(n) memory needs to be allocated out-of-place to store the stack. However,
-     * for small, simple tasks, like iterating an ObserverList in reverse, this is a useful way to
-     * concisely iterate a container in reverse order in a for-each loop.
-     *
-     * Example:
-     *
-     *      List<String> lines = ...;
-     *      // Prints lines in reverse order that they were added to the list.
-     *      for (String line : Itertools.reverse(lines)) {
-     *          Log.i(TAG, line);
-     *      }
-     */
-    public static <T> Iterable<T> reverse(Iterable<? extends T> iterable) {
-        return (() -> {
-            // Lazily iterate `iterable` only after reverse()'s `iterator()` method is called.
-            Stack<T> stack = new Stack<T>();
-            for (T item : iterable) {
-                stack.push(item);
-            }
-            return new Iterator<T>() {
-                @Override
-                public boolean hasNext() {
-                    return !stack.empty();
-                }
-                @Override
-                public T next() {
-                    return stack.pop();
-                }
-            };
-        });
-    }
-
     /**
      * Create an Iterable from an Iterator.
      *

chromecast/base/java/test/org/chromium/chromecast/base/ItertoolsTest.java

@@ -4,7 +4,6 @@
 
 package org.chromium.chromecast.base;
 
-import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.emptyIterable;
 import static org.junit.Assert.assertThat;
 
@@ -12,9 +11,6 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.BlockJUnit4ClassRunner;
 
-import org.chromium.chromecast.base.Inheritance.Base;
-import org.chromium.chromecast.base.Inheritance.Derived;
-
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
@@ -24,26 +20,6 @@ import java.util.List;
  */
 @RunWith(BlockJUnit4ClassRunner.class)
 public class ItertoolsTest {
-    @Test
-    public void testReverse() {
-        List<String> emptyList = new ArrayList<String>();
-        assertThat(Itertools.reverse(emptyList), emptyIterable());
-        List<String> singleItem = new ArrayList<>();
-        singleItem.add("a");
-        assertThat(Itertools.reverse(singleItem), contains("a"));
-        List<String> threeItems = new ArrayList<>();
-        threeItems.add("a");
-        threeItems.add("b");
-        threeItems.add("c");
-        assertThat(Itertools.reverse(threeItems), contains("c", "b", "a"));
-    }
-
-    @Test
-    public void testAssignReversedToIterableOfSuperclass() {
-        // Compile error if the generics are wrong.
-        Iterable<Base> reversed = Itertools.reverse(new ArrayList<Derived>());
-    }
-
     @Test
     public void testForEachLoopWithIterator() {
         Iterator<String> emptyIterator = new Iterator<String>() {