[Cronet] Change interface APIs to abstract classes

components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java

Index: components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java
diff --git a/components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java b/components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java
index ba57799ae4cce675244c55f9f698b90856eca14a..31c0b8d772875c8604a98e84799d0cf8fd7102b9 100644
--- a/components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java
+++ b/components/cronet/android/java/src/org/chromium/net/UploadDataProvider.java
@@ -16,13 +16,13 @@ import java.nio.ByteBuffer;
  * <p>An upload is either always chunked, across multiple uploads if the data
  * ends up being sent more than once, or never chunked.
  */
-public interface UploadDataProvider {
+public abstract class UploadDataProvider {

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

Although the guideline says we should *always* prefer abstract classes over
interfaces, I am not sure if we should change this one. I see why we might want
to change UrlRequestListener to an abstract class. But for UploadDataProvider,
if we do not know the form of underlying data (whether it's an array, buffer,
channel), it will be pretty hard to provide default states/implementations. Do
you have any use case in mind that we might need to augment this?

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

I'm just trying to future-proof us.  I could image wacky and weird things being
necessary in the future like:
   boolean isIdempotent()
   boolean canGZip()
   boolean isHangingPost()

     /**
      * If this is a non-chunked upload, returns the length of the upload. Must
      * always return -1 if this is a chunked upload.
      * @return the length of the upload for non-chunked uploads, -1 otherwise.
      */
-    public long getLength();
+    public abstract long getLength();
 
     /**
      * Reads upload data into {@code byteBuffer}. Upon completion, the buffer's
@@ -42,7 +42,7 @@ public interface UploadDataProvider {
      * @param byteBuffer The buffer to copy the read bytes into.
      * @throws IOException if any IOException occurred during the process.
      */
-    public void read(UploadDataSink uploadDataSink, ByteBuffer byteBuffer)
+    public abstract void read(UploadDataSink uploadDataSink, ByteBuffer byteBuffer)
             throws IOException;
 
     /**
@@ -65,6 +65,5 @@ public interface UploadDataProvider {
      *         completed, successfully or otherwise.
      * @throws IOException if any IOException occurred during the process.
      */
-    public void rewind(UploadDataSink uploadDataSink)
-            throws IOException;
+    public abstract void rewind(UploadDataSink uploadDataSink) throws IOException;
 }