Fix how ExifInterface creates VP8X chunks for WebP files

The current code reads alpha into an int, doesn't shift it back to the
least-significant-bit, and then shifts that value 4 more bits before
writing to the VP8X 'flags' byte. This results in setting the MSB of the
flags byte, which is a reserved bit that must always be zero, resulting
in an invalid file.

VP8X part of WebP spec:
https://developers.google.com/speed/webp/docs/riff_container#extended_file_format

Test: ExifInterfaceTest (after removing the suppression for this bug)

Bug: 253622642
Change-Id: I42469a479c94442eb395124c4eac174bd9ab6e09

media/java/android/media/ExifInterface.java

@@ -3825,7 +3825,7 @@ public class ExifInterface {
                     int widthAndHeight = 0;
                     int width = 0;
                     int height = 0;
-                    int alpha = 0;
+                    boolean alpha = false;
                     // Save VP8 frame data for later
                     byte[] vp8Frame = new byte[3];
 
@@ -3860,7 +3860,7 @@ public class ExifInterface {
                         width = ((widthAndHeight << 18) >> 18) + 1;
                         height = ((widthAndHeight << 4) >> 18) + 1;
                         // Retrieve alpha bit
-                        alpha = widthAndHeight & (1 << 3);
+                        alpha = (widthAndHeight & (1 << 28)) != 0;
                         bytesToRead -= (1 /* VP8L signature */ + 4);
                     }
 
@@ -3868,10 +3868,12 @@ public class ExifInterface {
                     nonHeaderOutputStream.write(WEBP_CHUNK_TYPE_VP8X);
                     nonHeaderOutputStream.writeInt(WEBP_CHUNK_TYPE_VP8X_DEFAULT_LENGTH);
                     byte[] data = new byte[WEBP_CHUNK_TYPE_VP8X_DEFAULT_LENGTH];
+                    // ALPHA flag
+                    if (alpha) {
+                        data[0] = (byte) (data[0] | (1 << 4));
+                    }
                     // EXIF flag
                     data[0] = (byte) (data[0] | (1 << 3));
-                    // ALPHA flag
-                    data[0] = (byte) (data[0] | (alpha << 4));
                     // VP8X stores Width - 1 and Height - 1 values
                     width -= 1;
                     height -= 1;