netty: support `status()` on Headers

* netty: support `status()` on Headers

Recent Netty change a91df58ca1
caused the `status()` method to be invoked, which AbstractHttp2Headers does not implement.
This change is necesary to upgrade to Netty 4.1.14

netty/src/main/java/io/grpc/netty/GrpcHttp2HeadersUtils.java

@@ -124,6 +124,11 @@ class GrpcHttp2HeadersUtils {
       return null;
     }
 
+    @Override
+    public CharSequence status() {
+      return get(Http2Headers.PseudoHeaderName.STATUS.value());
+    }
+
     @Override
     public List<CharSequence> getAll(CharSequence csName) {
       AsciiString name = requireAsciiString(csName);

netty/src/main/java/io/grpc/netty/GrpcHttp2OutboundHeaders.java

@@ -66,6 +66,16 @@ final class GrpcHttp2OutboundHeaders extends AbstractHttp2Headers {
     this.preHeaders = preHeaders;
   }
 
+  @Override
+  @SuppressWarnings("ReferenceEquality") // STATUS.value() never changes.
+  public CharSequence status() {
+    // preHeaders is never null.  It has status as the first element or not at all.
+    if (preHeaders.length >= 2 && preHeaders[0] == Http2Headers.PseudoHeaderName.STATUS.value()) {
+      return preHeaders[1];
+    }
+    return null;
+  }
+
   @Override
   public Iterator<Entry<CharSequence, CharSequence>> iterator() {
     return new Itr();