HBASE-25425 Some notes on RawCell

(cherry picked from commit 9aac9db)

Change-Id: I72daba84319cb0d42e321b9ec6f2d784fe6020d8

hbase-client/src/main/java/org/apache/hadoop/hbase/client/Mutation.java

@@ -40,7 +40,6 @@
 import org.apache.hadoop.hbase.IndividualBytesFieldCell;
 import org.apache.hadoop.hbase.KeyValue;
 import org.apache.hadoop.hbase.PrivateCellUtil;
-import org.apache.hadoop.hbase.RawCell;
 import org.apache.hadoop.hbase.Tag;
 import org.apache.hadoop.hbase.exceptions.DeserializationException;
 import org.apache.hadoop.hbase.io.HeapSize;
@@ -932,25 +931,16 @@ public byte getTypeByte() {
 
     @Override
     public Optional<Tag> getTag(byte type) {
-      if (cell instanceof RawCell) {
-        return ((RawCell) cell).getTag(type);
-      }
       return PrivateCellUtil.getTag(cell, type);
     }
 
     @Override
     public Iterator<Tag> getTags() {
-      if (cell instanceof RawCell) {
-        return ((RawCell) cell).getTags();
-      }
       return PrivateCellUtil.tagsIterator(cell);
     }
 
     @Override
     public byte[] cloneTags() {
-      if (cell instanceof RawCell) {
-        return ((RawCell) cell).cloneTags();
-      }
       return PrivateCellUtil.cloneTags(cell);
     }
 

hbase-common/src/main/java/org/apache/hadoop/hbase/RawCell.java

@@ -24,8 +24,12 @@
 import org.apache.yetus.audience.InterfaceAudience;
 
 /**
- * An extended version of cell that gives more power to CPs
+ * An extended version of Cell that allows CPs manipulate Tags.
  */
+// Added by HBASE-19092 to expose Tags to CPs (history server) w/o exposing ExtendedCell.
+// Why is this in hbase-common and not in hbase-server where it is used?
+// RawCell is an odd name for a class that is only for CPs that want to manipulate Tags on
+// server-side only w/o exposing ExtendedCell -- super rare, super exotic.
 @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
 public interface RawCell extends Cell {
   static final int MAX_TAGS_LENGTH = (2 * Short.MAX_VALUE) + 1;