fix ax unique id may return id bigger than the max value

Change-Id: I0a04d7537c9e313e2c5e5157f836b4b28de44216
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2616901Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842753}

ui/accessibility/platform/ax_unique_id.cc

@@ -46,7 +46,7 @@ int32_t AXUniqueId::GetNextAXUniqueId(const int32_t max_id) {
 
   const int32_t prev_id = current_id;
   do {
-    if (current_id == max_id) {
+    if (current_id >= max_id) {
       current_id = 1;
       has_wrapped = true;
     } else {

ui/accessibility/platform/ax_unique_id_unittest.cc

@@ -53,4 +53,22 @@ TEST(AXPlatformUniqueIdTest, UnassignedIdsAreReused) {
   EXPECT_EQ(ids[kIdToReplace]->Get(), expected_id);
 }
 
+TEST(AXPlatformUniqueIdTest, DoesCreateCorrectId) {
+  int kLargerThanMaxId = kMaxId * 2;
+  std::unique_ptr<AXUniqueId> ids[kLargerThanMaxId];
+  // Creates and releases to fill up the internal static counter.
+  for (int i = 0; i < kLargerThanMaxId; i++) {
+    ids[i] = std::make_unique<AXUniqueId>();
+  }
+  for (int i = 0; i < kLargerThanMaxId; i++) {
+    ids[i].reset(nullptr);
+  }
+  // Creates an unique id whose max value is less than the internal
+  // static counter.
+  std::unique_ptr<AXTestSmallBankUniqueId> unique_id =
+      std::make_unique<AXTestSmallBankUniqueId>();
+
+  EXPECT_LE(unique_id->Get(), kMaxId);
+}
+
 }  // namespace ui