Add CompletedEpisodes counter (#3724)

Project/Assets/ML-Agents/Examples/SharedAssets/Scripts/ModelOverrider.cs

         {
             if (m_MaxEpisodes > 0)
             {
-                if (m_NumSteps > m_MaxEpisodes * m_Agent.maxStep)
+                // For Agents without maxSteps, exit as soon as we've hit the target number of episodes.
+                // For Agents that specify maxStep, also make sure we've gone at least that many steps.
+                // Since we exit as soon as *any* Agent hits its target, the maxSteps condition keeps us running
+                // a bit longer in case there's an early failure.
+                if (m_Agent.CompletedEpisodes >= m_MaxEpisodes && m_NumSteps > m_MaxEpisodes * m_Agent.maxStep)
                 {
                     Application.Quit(0);
                 }

com.unity.ml-agents/Runtime/Agent.cs

         /// their own experience.
         int m_StepCount;
 
+        /// Number of times the Agent has completed an episode.
+        int m_CompletedEpisodes;
+
         /// Episode identifier each agent receives. It is used
         /// to separate between different agents in the environment.
         /// This Id will be changed every time the Agent resets.
 
             if (doneReason != DoneReason.Disabled)
             {
-                // We don't want to udpate the reward stats when the Agent is disabled, because this will make
+                // We don't want to update the reward stats when the Agent is disabled, because this will make
+                m_CompletedEpisodes++;
                 UpdateRewardStats();
             }
 
         public int StepCount
         {
             get { return m_StepCount; }
+        }
+
+        /// <summary>
+        /// Returns the number of episodes that the Agent has completed (either <see cref="Agent.EndEpisode()"/>
+        /// was called, or maxSteps was reached).
+        /// </summary>
+        /// <returns>
+        /// Current episode count.
+        /// </returns>
+        public int CompletedEpisodes
+        {
+            get { return m_CompletedEpisodes; }
         }
 
         /// <summary>

com.unity.ml-agents/Tests/Editor/MLAgentsEditModeTest.cs

             var expectedAgentActionForEpisode = 0;
             var expectedCollectObsCalls = 0;
             var expectedCollectObsCallsForEpisode = 0;
+            var expectedCompletedEpisodes = 0;
 
             for (var i = 0; i < 15; i++)
             {
                     expectedAgentActionForEpisode = 0;
                     expectedCollectObsCallsForEpisode = 0;
                     expectedAgentStepCount = 0;
+                    expectedCompletedEpisodes++;
                 }
                 aca.EnvironmentStep();
 
                 Assert.AreEqual(expectedAgentActionForEpisode, agent1.agentActionCallsForEpisode);
                 Assert.AreEqual(expectedCollectObsCalls, agent1.collectObservationsCalls);
                 Assert.AreEqual(expectedCollectObsCallsForEpisode, agent1.collectObservationsCallsForEpisode);
+                Assert.AreEqual(expectedCompletedEpisodes, agent1.CompletedEpisodes);
             }
         }