[Cronet] Change interface APIs to abstract classes

components/cronet/README.md

Index: components/cronet/README.md
diff --git a/components/cronet/README.md b/components/cronet/README.md
index 22aca16a4a4363afc2a88044b36175365beaa327..87e6aec79ea80352af3b052ce8c1cc1a2c99377c 100644
--- a/components/cronet/README.md
+++ b/components/cronet/README.md
@@ -8,10 +8,10 @@ API as well as support for the [java.net.HttpURLConnection] API.
 This document gives a brief introduction to using these two Java APIs.
 
 ### Basics
-First you will need to implement the `UrlRequestListener` interface to handle
+First you will need to implement the `UrlRequestListener` class to handle

[xunjieli, 2015/09/03 04:32:02]

I am not sure... Should we also use "extend" instead of "implement" in
sentences? Loosely speaking, "implement" does convey the right idea, so I am not
sure if we need to change it here and elsewhere to use "extend" instead,  though
these two words are a bit different in the Java land and we probably should
avoid confusing those two when explaining?

[pauljensen, 2015/09/11 15:20:41]

Ya, I think we should stick with "implement" in English while the class is
mostly abstract members.  Even if only a minority of the class members are
abstract, "extend" doesn't seem to imply the right action, more like "override";
but for now when it's 100% abstract members, I think "implement" is the best
description of the action embedders will take.

Now that I read it, saying "implement the class" doesn't sound right; embedders
will be implementing a subclass.  I've reworded. PTAL.

[xunjieli, 2015/09/11 16:26:35]

Acknowledged. SGTM

 events during the lifetime of a request. For example:
 
-    class MyListener implements UrlRequestListener {
+    class MyListener extends UrlRequestListener {
         @Override
         public void onReceivedRedirect(UrlRequest request,
                 ResponseInfo responseInfo, String newLocationUrl) {
@@ -78,7 +78,7 @@ Make a request like this:
     request.start();
 
 In the above example, `MyListener` implements the `UrlRequestListener`

[xunjieli, 2015/09/03 04:32:02]

Here, I also wonder whether we should s/implements/extends.

[pauljensen, 2015/09/11 15:20:41]

I feel the same way as on line 11.  I reworded like I did on line 11.

-interface. The request is started asynchronously. When the response is ready
+class. The request is started asynchronously. When the response is ready
 (fully or partially), and in the event of failures or redirects,
 `listener`'s methods will be invoked on `executor`'s thread to inform the
 client of the request state and/or response information.
@@ -104,7 +104,7 @@ which signals the completion of the request.
     request.start();
 
 In the above example, `MyUploadDataProvider` implements the

[xunjieli, 2015/09/03 04:32:02]

And here.

[pauljensen, 2015/09/11 15:20:41]

I feel the same way as on line 11.  I reworded like I did on line 11.

-`UploadDataProvider` interface. When Cronet is ready to send the request body,
+`UploadDataProvider` class. When Cronet is ready to send the request body,
 `myUploadDataProvider.read(UploadDataSink uploadDataSink,
 ByteBuffer byteBuffer)` will be invoked. The client will need to write the
 request body into `byteBuffer`. Once the client is done writing into