[Cronet] Clear mock cert verifier reference in CronetEngine.Builder

components/cronet/android/api/src/org/chromium/net/CronetEngine.java

Index: components/cronet/android/api/src/org/chromium/net/CronetEngine.java
diff --git a/components/cronet/android/api/src/org/chromium/net/CronetEngine.java b/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
index 5047ab6e23f289342e02621113f98ffaaf7afa9d..6e7d1e0940ccc2fa4668cc24373cd866e90866ea 100644
--- a/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
+++ b/components/cronet/android/api/src/org/chromium/net/CronetEngine.java
@@ -382,7 +382,11 @@ public abstract class CronetEngine {
          * Build a {@link CronetEngine} using this builder's configuration.
          */
         public CronetEngine build() {
-            return createContext(this);
+            CronetEngine engine = createContext(this);
+            // Clear MOCK_CERT_VERIFIER reference if there is any, since
+            // the ownership has been transferred to the engine.
+            mConfig.remove(CronetEngineBuilderList.MOCK_CERT_VERIFIER);
+            return engine;
         }
     }