Minor convergence with server-side code.

This CL was intended to change ssize() to size(), but the change to use
ssize() was not merged, so this CL is mostly a no-op (except for some
minor convergence opportunities).

This CL lands server change 177314606 by sbenza.

BUG=488484

Change-Id: I14358dc6888026ad59fd0a8e48b52147637b6c51
Reviewed-on: https://chromium-review.googlesource.com/809846
Commit-Queue: Bence Béky <bnc@chromium.org>
Reviewed-by: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522176}

net/http2/hpack/decoder/hpack_decoder_string_buffer.cc

@@ -168,7 +168,7 @@ void HpackDecoderStringBuffer::BufferStringIfUnbuffered() {
   if (state_ != State::RESET && backing_ == Backing::UNBUFFERED) {
     DVLOG(2) << "HpackDecoderStringBuffer buffering string of length "
              << value_.size();
-    value_.CopyToString(&buffer_);
+    buffer_.assign(value_.data(), value_.size());
     if (state_ == State::COMPLETE) {
       value_ = buffer_;
     }

net/http2/test_tools/frame_parts.cc

@@ -509,7 +509,7 @@ AssertionResult FrameParts::AppendString(Http2StringPiece source,
   target->append(source.data(), source.size());
   if (opt_length != nullptr) {
     VERIFY_TRUE(*opt_length) << "Length is not set yet\n" << *this;
-    VERIFY_LE(target->size(), static_cast<size_t>(opt_length->value()))
+    VERIFY_LE(target->size(), opt_length->value())
         << "String too large; source.size() = " << source.size() << "\n"
         << *this;
   }