Fix iterator remove bug.

See the test case for details of the bug.

To put an end to these bugs I decided to simplify with a small
additional cost on removal.
Simpler is saner...

Change-Id: If64056d90b71c226b9c07ee99ab5c8ff76ded57d
Review-Link: https://gwt-review.googlesource.com/#/c/13489/

user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java

diff --git a/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java b/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
index 19a0011..1d78932 100644
--- a/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
+++ b/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
@@ -75,6 +75,7 @@
       Entry<K, V> entry = chain[i];
       if (host.equals(key, entry.getKey())) {
         if (chain.length == 1) {
+          ArrayHelper.setLength(chain, 0);
           // remove the whole array
           backingMap.delete(hashCode);
         } else {
@@ -112,7 +113,6 @@
       final InternalJsIterator<Object> chains = backingMap.entries();
       int itemIndex = 0;
       Entry<K, V>[] chain = newEntryChain();
-      Entry<K, V>[] lastChain = null;
       Entry<K, V> lastEntry = null;
 
       @Override
@@ -134,7 +134,6 @@
       public Entry<K, V> next() {
         checkElement(hasNext());
 
-        lastChain = chain;
         lastEntry = chain[itemIndex++];
         return lastEntry;
       }
@@ -143,14 +142,11 @@
       public void remove() {
         checkState(lastEntry != null);
 
-        boolean isLastChain = itemIndex == lastChain.length;
         InternalHashCodeMap.this.remove(lastEntry.getKey());
-
-        // If this was not the last item in the chain, our itemIndex just jumped an item.
-        if (!isLastChain) {
+        // Unless we are in a new chain, all items have shifted so our itemIndex should as well...
+        if (itemIndex != 0) {
           itemIndex--;
         }
-
         lastEntry = null;
       }
     };

user/test/com/google/gwt/emultest/java/util/HashMapTest.java

diff --git a/user/test/com/google/gwt/emultest/java/util/HashMapTest.java b/user/test/com/google/gwt/emultest/java/util/HashMapTest.java
index 28f232f..81054aa 100644
--- a/user/test/com/google/gwt/emultest/java/util/HashMapTest.java
+++ b/user/test/com/google/gwt/emultest/java/util/HashMapTest.java
@@ -758,7 +758,7 @@
   }
 
   // see: https://github.com/gwtproject/gwt/issues/9184
-  public void testIterationWithCollidingHashCodes() {
+  public void testIteration_withCollidingHashCodes() {
 
     Object firstKey = createObjectWithHashCode(1);
     Object secondKey = createObjectWithHashCode(1);
@@ -793,7 +793,7 @@
   }
 
   // see: https://github.com/gwtproject/gwt/issues/9184
-  public void testIterationWithCollidingHashCodes_FullIteration() {
+  public void testIteration_withCollidingHashCodesAndFullIteration() {
 
     List<Object> keys = new ArrayList<>();
     HashMap<Object, String> testMap = new HashMap<>();
@@ -818,6 +818,22 @@
     assertTrue(keys.isEmpty());
   }
 
+  public void testIteration_hasNextThenRemove() {
+    HashMap<Object, String> testMap = new HashMap<>();
+    testMap.put(createObjectWithHashCode(1), "one");
+    testMap.put(createObjectWithHashCode(2), "two");
+
+    Iterator<Object> it = testMap.keySet().iterator();
+    it.next();
+    assertTrue("iterator should have next after first", it.hasNext());
+    it.remove();
+    assertTrue("iterator should have next after removal", it.hasNext());
+
+    it.next();
+    it.remove();
+    assertFalse(it.hasNext());
+  }
+
   private Object createObjectWithHashCode(final int hashCode) {
     return new Object() {
       @Override