Make ImageDecoder#getSampledSize private

Bug: 152322291
Test: make

I originally added this thinking a client might use the following
pattern:

    Size size = decoder.getSampledSize(sampleSize);
    decoder.setTargetSize(size.getWidth(), size.getHeight());

But this is unnecessary. The client can directly call:

    decoder.setTargetSampleSize(sampleSize);

OTOH, if the client wanted to use a crop, too, then it would be useful
to know the exact sampled size. That could also be satisfied by adding
accessors that return the target size.

Change-Id: Id61907a8268f424d70503598d5bf844cde469d60

graphics/java/android/graphics/ImageDecoder.java

@@ -1072,11 +1072,9 @@ public final class ImageDecoder implements AutoCloseable {
      *  @param sampleSize Sampling rate of the encoded image.
      *  @return {@link android.util.Size} of the width and height after
      *      sampling.
-     *
-     *  @hide
      */
     @NonNull
-    public Size getSampledSize(int sampleSize) {
+    private Size getSampledSize(int sampleSize) {
         if (sampleSize <= 0) {
             throw new IllegalArgumentException("sampleSize must be positive! "
                     + "provided " + sampleSize);