Rename SpdyHeaderBlock to Http2HeaderBlock.

Salvaged from a botched Zwingli attempt:
http://refactor/16032281396283088571 created by go/Zwingli

Tested:
    TAP for global presubmit queue passed after automated deflaking of failures: http://mondo/deflaker/run/9a9c8d4e-50d0-47e0-970b-4b6c24ace2d7 http://mondo/deflaker/run/32a00ba5-16fa-4c78-9e10-afa7c56abc61
    http://test/OCL:338336205:BASE:339106963:1603774283861:13fcf12c
PiperOrigin-RevId: 339252455
Change-Id: Icce13789ba4b6e74894b0715ec897fc61aba9993
diff --git a/spdy/core/spdy_test_utils.h b/spdy/core/spdy_test_utils.h
index aaaa65a..c6390a7 100644
--- a/spdy/core/spdy_test_utils.h
+++ b/spdy/core/spdy_test_utils.h
@@ -18,7 +18,7 @@
 namespace spdy {
 
 inline bool operator==(absl::string_view x,
-                       const SpdyHeaderBlock::ValueProxy& y) {
+                       const Http2HeaderBlock::ValueProxy& y) {
   return y.operator==(x);
 }
 
@@ -54,14 +54,14 @@
   void OnHeaderBlockEnd(size_t header_bytes_parsed,
                         size_t compressed_header_bytes_parsed) override;
 
-  const SpdyHeaderBlock& decoded_block() const { return block_; }
+  const Http2HeaderBlock& decoded_block() const { return block_; }
   size_t header_bytes_parsed() const { return header_bytes_parsed_; }
   size_t compressed_header_bytes_parsed() const {
     return compressed_header_bytes_parsed_;
   }
 
  private:
-  SpdyHeaderBlock block_;
+  Http2HeaderBlock block_;
   size_t header_bytes_parsed_ = 0;
   size_t compressed_header_bytes_parsed_ = 0;
 };