[Cronet] Better document Experimental Cronet classes

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

Index: components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java
diff --git a/components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java b/components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java
index 6d034ad1314621c3194827b479e625f156ddb3b4..cdf54bc19d7a8359e8401c21720973f6ece077de 100644
--- a/components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java
+++ b/components/cronet/android/api/src/org/chromium/net/ExperimentalCronetEngine.java
@@ -15,9 +15,13 @@ import java.util.Set;
 import java.util.concurrent.Executor;
 
 /**
- * {@link CronetEngine} that exposes experimental features. Use {@link Builder} to build an
- * instance of this class. Every instance of {@link CronetEngine} can be casted to an instance
- * of this class.
+ * {@link CronetEngine} that exposes experimental features. To obtain an
+ * instance of this class, cast a {@code CronetEngine} to this type. Every
+ * instance of {@code CronetEngine} can be cast to an instance of this class,
+ * as they are backed by the same implementation and hence perform identically.
+ * Instances of this class are not meant for general use, but instead only
+ * to access experimental features. Experimental features may be deprecated in the
+ * future. Use at your own risk.
  *
  * {@hide since this class exposes experimental features that should be hidden.}
  */
@@ -70,7 +74,10 @@ public abstract class ExperimentalCronetEngine extends CronetEngine {
     public static final int EFFECTIVE_CONNECTION_TYPE_4G = 5;
 
     /**
-     * Builder for building {@link ExperimentalCronetEngine}.
+     * A version of {@link CronetEngine.Builder} that exposes experimental
+     * features. Instances of this class are not meant for general use, but
+     * instead only to access experimental features. Experimental features
+     * may be deprecated in the future. Use at your own risk.
      */
     public static class Builder extends CronetEngine.Builder {
         /**