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_framer.cc b/spdy/core/spdy_framer.cc
index e5619df..d425bdd 100644
--- a/spdy/core/spdy_framer.cc
+++ b/spdy/core/spdy_framer.cc
@@ -45,7 +45,7 @@
 // The size of one parameter in SETTINGS frame.
 const size_t kOneSettingParameterSize = 6;
 
-size_t GetUncompressedSerializedLength(const SpdyHeaderBlock& headers) {
+size_t GetUncompressedSerializedLength(const Http2HeaderBlock& headers) {
   const size_t num_name_value_pairs_size = sizeof(uint32_t);
   const size_t length_of_name_size = num_name_value_pairs_size;
   const size_t length_of_value_size = num_name_value_pairs_size;