Expose size() and isEmpty() in ObserverList.

BUG=347558

Review URL: https://codereview.chromium.org/198093004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257094 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 110 insertions, 15 deletions

diff --git a/base/android/java/src/org/chromium/base/ObserverList.java b/base/android/java/src/org/chromium/base/ObserverList.java
index 012f475..54f8517 100644
--- a/base/android/java/src/org/chromium/base/ObserverList.java
+++ b/base/android/java/src/org/chromium/base/ObserverList.java
@@ -45,6 +45,7 @@ public class ObserverList<E> implements Iterable<E> {
 
     public final List<E> mObservers = new ArrayList<E>();
     private int mIterationDepth = 0;
+    private int mCount = 0;
 
     public ObserverList() {}
 
@@ -64,7 +65,11 @@ public class ObserverList<E> implements Iterable<E> {
 
         // Structurally modifying the underlying list here. This means we
         // cannot use the underlying list's iterator to iterate over the list.
-        return mObservers.add(obs);
+        boolean result = mObservers.add(obs);
+        assert result == true;
+
+        ++mCount;
+        return true;
     }
 
     /**
@@ -88,6 +93,8 @@ public class ObserverList<E> implements Iterable<E> {
         } else {
             mObservers.set(index, null);
         }
+        --mCount;
+        assert mCount >= 0;
 
         return true;
     }
@@ -97,6 +104,8 @@ public class ObserverList<E> implements Iterable<E> {
     }
 
     public void clear() {
+        mCount = 0;
+
         if (mIterationDepth == 0) {
             mObservers.clear();
             return;
@@ -123,6 +132,21 @@ public class ObserverList<E> implements Iterable<E> {
     }
 
     /**
+     * Returns the number of observers currently registered in the ObserverList.
+     * This is equivalent to the number of non-empty spaces in |mObservers|.
+     */
+    public int size() {
+        return mCount;
+    }
+
+    /**
+     * Returns true if the ObserverList contains no observers.
+     */
+    public boolean isEmpty() {
+        return mCount == 0;
+    }
+
+    /**
      * Compact the underlying list be removing null elements.
      * <p/>
      * Should only be called when mIterationDepth is zero.
@@ -147,7 +171,11 @@ public class ObserverList<E> implements Iterable<E> {
             compact();
     }
 
-    private int getSize() {
+    /**
+     * Returns the size of the underlying storage of the ObserverList.
+     * It will take into account the empty spaces inside |mObservers|.
+     */
+    private int capacity() {
         return mObservers.size();
     }
 
@@ -162,14 +190,14 @@ public class ObserverList<E> implements Iterable<E> {
 
         private ObserverListIterator() {
             ObserverList.this.incrementIterationDepth();
-            mListEndMarker = ObserverList.this.getSize();
+            mListEndMarker = ObserverList.this.capacity();
         }
 
         @Override
         public void rewind() {
             compactListIfNeeded();
             ObserverList.this.incrementIterationDepth();
-            mListEndMarker = ObserverList.this.getSize();
+            mListEndMarker = ObserverList.this.capacity();
             mIsExhausted = false;
             mIndex = 0;
         }
diff --git a/base/android/javatests/src/org/chromium/base/ObserverListTest.java b/base/android/javatests/src/org/chromium/base/ObserverListTest.java
index f999168..599534a 100644
--- a/base/android/javatests/src/org/chromium/base/ObserverListTest.java
+++ b/base/android/javatests/src/org/chromium/base/ObserverListTest.java
@@ -252,4 +252,80 @@ public class ObserverListTest extends InstrumentationTestCase {
         assertTrue(observerList.removeObserver(a));
         assertFalse(observerList.removeObserver(null));
     }
+
+    @SmallTest
+    @Feature({"Android-AppBase"})
+    public void testSize() {
+        ObserverList<Object> observerList = new ObserverList<Object>();
+
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+
+        observerList.addObserver(null);
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+
+        Object a = new Object();
+        observerList.addObserver(a);
+        assertEquals(1, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.addObserver(a);
+        assertEquals(1, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.addObserver(null);
+        assertEquals(1, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        Object b = new Object();
+        observerList.addObserver(b);
+        assertEquals(2, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.removeObserver(null);
+        assertEquals(2, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.removeObserver(new Object());
+        assertEquals(2, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.removeObserver(b);
+        assertEquals(1, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.removeObserver(b);
+        assertEquals(1, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.removeObserver(a);
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+
+        observerList.removeObserver(a);
+        observerList.removeObserver(b);
+        observerList.removeObserver(null);
+        observerList.removeObserver(new Object());
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+
+        observerList.addObserver(new Object());
+        observerList.addObserver(new Object());
+        observerList.addObserver(new Object());
+        observerList.addObserver(a);
+        assertEquals(4, observerList.size());
+        assertFalse(observerList.isEmpty());
+
+        observerList.clear();
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+
+        observerList.removeObserver(a);
+        observerList.removeObserver(b);
+        observerList.removeObserver(null);
+        observerList.removeObserver(new Object());
+        assertEquals(0, observerList.size());
+        assertTrue(observerList.isEmpty());
+    }
 }
diff --git a/content/public/android/java/src/org/chromium/content/browser/ScreenOrientationListener.java b/content/public/android/java/src/org/chromium/content/browser/ScreenOrientationListener.java
index 6125b70..b5068aa 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ScreenOrientationListener.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ScreenOrientationListener.java
@@ -144,11 +144,6 @@ class ScreenOrientationListener {
     private final ObserverList<ScreenOrientationObserver> mObservers =
             new ObserverList<ScreenOrientationObserver>();
 
-    // Number of observers currently in |mObservers|.
-    // TODO(mlamouri): hopefully, we can get ObserverList to provide that,
-    // http://crbug.com/347558
-    private int mObserverCount;
-
     // mOrientation will be updated every time the orientation changes. When not
     // listening for changes, the value will be invalid and will be updated when
     // starting to listen again.
@@ -210,10 +205,9 @@ class ScreenOrientationListener {
             Log.w(TAG, "Adding an observer that is already present!");
             return;
         }
-        mObserverCount++;
 
         // If we got our first observer, we should start listening.
-        if (mObserverCount == 1) {
+        if (mObservers.size() == 1) {
             updateOrientation();
             mBackend.startListening();
         }
@@ -240,14 +234,11 @@ class ScreenOrientationListener {
             Log.w(TAG, "Removing an inexistent observer!");
             return;
         }
-        mObserverCount--;
 
-        if (mObserverCount == 0) {
+        if (mObservers.isEmpty()) {
             // The last observer was removed, we should just stop listening.
             mBackend.stopListening();
         }
-
-        assert mObserverCount >= 0;
     }
 
     /**