Don't put timers with ID == 0 into the global timer map.

testing/embedder_test_timer_handling_delegate.h

Index: testing/embedder_test_timer_handling_delegate.h
diff --git a/testing/embedder_test_timer_handling_delegate.h b/testing/embedder_test_timer_handling_delegate.h
index 709dd22c1723f0cf299c98723aa84c647ab45339..31966159eb95e9afc292bbae711b9e2f9e0752d7 100644
--- a/testing/embedder_test_timer_handling_delegate.h
+++ b/testing/embedder_test_timer_handling_delegate.h
@@ -38,9 +38,11 @@ class EmbedderTestTimerHandlingDelegate : public EmbedderTest::Delegate {
   }
 
   int SetTimer(int msecs, TimerCallback fn) override {
-    expiry_to_timer_map_.insert(std::pair<int, Timer>(
-        msecs + fake_elapsed_msecs_, {++next_timer_id_, msecs, fn}));
-    return next_timer_id_;
+    int id = fail_next_timer_ ? 0 : ++next_timer_id_;
+    expiry_to_timer_map_.insert(
+        std::pair<int, Timer>(msecs + fake_elapsed_msecs_, {id, msecs, fn}));
+    fail_next_timer_ = false;
+    return id;
   }
 
   void KillTimer(int id) override {
@@ -73,8 +75,11 @@ class EmbedderTestTimerHandlingDelegate : public EmbedderTest::Delegate {
 
   const std::vector<AlertRecord>& GetAlerts() const { return alerts_; }
 
+  void SetFailNextTimer() { fail_next_timer_ = true; }
+
  protected:
   std::multimap<int, Timer> expiry_to_timer_map_;  // Keyed by timeout.
+  bool fail_next_timer_ = false;
   int next_timer_id_ = 0;
   int fake_elapsed_msecs_ = 0;
   std::vector<AlertRecord> alerts_;