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

testing/embedder_test_timer_handling_delegate.h

 // Copyright 2015 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TESTING_EMBEDDER_TEST_TIMER_HANDLING_DELEGATE_H_
 #define TESTING_EMBEDDER_TEST_TIMER_HANDLING_DELEGATE_H_
 
 #include <map>
 #include <string>
 #include <utility>
@@ skipping 20 matching lines @@
   int Alert(FPDF_WIDESTRING message,
             FPDF_WIDESTRING title,
             int type,
             int icon) override {
     alerts_.push_back(
         {GetPlatformWString(message), GetPlatformWString(title), type, icon});
     return 0;
   }
 
   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 {
     for (auto iter = expiry_to_timer_map_.begin();
          iter != expiry_to_timer_map_.end(); ++iter) {
       if (iter->second.id == id) {
         expiry_to_timer_map_.erase(iter);
         break;
       }
     }
@@ skipping 12 matching lines @@
       Timer t = iter->second;
       expiry_to_timer_map_.erase(iter);
       expiry_to_timer_map_.insert(
           std::pair<int, Timer>(fake_elapsed_msecs_ + t.interval, t));
       t.fn(t.id);  // Fire timer.
     }
   }
 
   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_;
 };
 
 #endif  // TESTING_EMBEDDER_TEST_TIMER_HANDLING_DELEGATE_H_