Remove TestFrameSequence::MetadataBlockForPayload().

Metadata tests compare HeaderBlock(payload) to HeaderBlock(payload). We can
simplify the equation by removing the HeaderBlock() wrapping on both sides.
This change aligns with the header block encoding and decoding of metadata
happening above the nghttp2 extension layer/the OgHttp2Session metadata layer.
This change is also a prefactor for sending empty metadata payloads in tests.

PiperOrigin-RevId: 420864596
diff --git a/http2/adapter/nghttp2_adapter_test.cc b/http2/adapter/nghttp2_adapter_test.cc
index 0d9ee33..ced8a82 100644
--- a/http2/adapter/nghttp2_adapter_test.cc
+++ b/http2/adapter/nghttp2_adapter_test.cc
@@ -3039,11 +3039,9 @@
 
   const int64_t result = adapter->ProcessBytes(frames);
   EXPECT_EQ(frames.size(), result);
-  EXPECT_EQ(TestFrameSequence::MetadataBlockForPayload(
-                "Example connection metadata in multiple frames"),
+  EXPECT_EQ("Example connection metadata in multiple frames",
             absl::StrJoin(visitor.GetMetadata(0), ""));
-  EXPECT_EQ(TestFrameSequence::MetadataBlockForPayload(
-                "Some stream metadata that's also sent in multiple frames"),
+  EXPECT_EQ("Some stream metadata that's also sent in multiple frames",
             absl::StrJoin(visitor.GetMetadata(1), ""));
 }
 
diff --git a/http2/adapter/oghttp2_adapter_test.cc b/http2/adapter/oghttp2_adapter_test.cc
index 302e745..5a82c97 100644
--- a/http2/adapter/oghttp2_adapter_test.cc
+++ b/http2/adapter/oghttp2_adapter_test.cc
@@ -2443,11 +2443,9 @@
 
   const int64_t result = adapter->ProcessBytes(frames);
   EXPECT_EQ(frames.size(), static_cast<size_t>(result));
-  EXPECT_EQ(TestFrameSequence::MetadataBlockForPayload(
-                "Example connection metadata in multiple frames"),
+  EXPECT_EQ("Example connection metadata in multiple frames",
             absl::StrJoin(visitor.GetMetadata(0), ""));
-  EXPECT_EQ(TestFrameSequence::MetadataBlockForPayload(
-                "Some stream metadata that's also sent in multiple frames"),
+  EXPECT_EQ("Some stream metadata that's also sent in multiple frames",
             absl::StrJoin(visitor.GetMetadata(1), ""));
 }
 
diff --git a/http2/adapter/test_frame_sequence.cc b/http2/adapter/test_frame_sequence.cc
index 4a99807..074e3dd 100644
--- a/http2/adapter/test_frame_sequence.cc
+++ b/http2/adapter/test_frame_sequence.cc
@@ -157,18 +157,16 @@
 TestFrameSequence& TestFrameSequence::Metadata(Http2StreamId stream_id,
                                                absl::string_view payload,
                                                bool multiple_frames) {
-  const std::string encoded_payload = MetadataBlockForPayload(payload);
   if (multiple_frames) {
-    const size_t pos = encoded_payload.size() / 2;
+    const size_t pos = payload.size() / 2;
     frames_.push_back(absl::make_unique<spdy::SpdyUnknownIR>(
-        stream_id, kMetadataFrameType, 0, encoded_payload.substr(0, pos)));
+        stream_id, kMetadataFrameType, 0, std::string(payload.substr(0, pos))));
     frames_.push_back(absl::make_unique<spdy::SpdyUnknownIR>(
         stream_id, kMetadataFrameType, kMetadataEndFlag,
-        encoded_payload.substr(pos)));
+        std::string(payload.substr(pos))));
   } else {
     frames_.push_back(absl::make_unique<spdy::SpdyUnknownIR>(
-        stream_id, kMetadataFrameType, kMetadataEndFlag,
-        std::move(encoded_payload)));
+        stream_id, kMetadataFrameType, kMetadataEndFlag, std::string(payload)));
   }
   return *this;
 }
@@ -186,16 +184,6 @@
   return result;
 }
 
-std::string TestFrameSequence::MetadataBlockForPayload(
-    absl::string_view payload) {
-  // Encode the payload using a header block.
-  spdy::SpdyHeaderBlock block;
-  block["example-payload"] = payload;
-  spdy::HpackEncoder encoder;
-  encoder.DisableCompression();
-  return encoder.EncodeHeaderBlock(block);
-}
-
 }  // namespace test
 }  // namespace adapter
 }  // namespace http2
diff --git a/http2/adapter/test_frame_sequence.h b/http2/adapter/test_frame_sequence.h
index 88f0af9..0eddf41 100644
--- a/http2/adapter/test_frame_sequence.h
+++ b/http2/adapter/test_frame_sequence.h
@@ -61,8 +61,6 @@
 
   std::string Serialize();
 
-  static std::string MetadataBlockForPayload(absl::string_view);
-
  private:
   std::string preface_;
   std::vector<std::unique_ptr<spdy::SpdyFrameIR>> frames_;