Remove unnecessary local variable in CreateIterator().

Also add one comment.

No functional change.

This CL lands server change 162922389 by bnc.
This CL lands server change 162991254 by yasong.

BUG=488484

Change-Id: I33889d0895da9c7a322cb8a11e0da3e4e0697470
Reviewed-on: https://chromium-review.googlesource.com/591774Reviewed-by: Bence Béky <bnc@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490760}

net/spdy/core/priority_write_scheduler.h

@@ -35,6 +35,8 @@ class PriorityWriteSchedulerPeer;
 // for each priority value.  Each PriorityInfo contains a list of streams of
 // that priority that are ready to write, as well as a timestamp of the last
 // I/O event that occurred for a stream of that priority.
+//
+// DO NOT USE. Deprecated.
 template <typename StreamIdType>
 class PriorityWriteScheduler : public WriteScheduler<StreamIdType> {
  public:

net/spdy/core/spdy_framer.cc

@@ -417,30 +417,26 @@ const SpdyFrameIR& SpdyFramer::SpdyControlFrameIterator::GetIR() const {
 std::unique_ptr<SpdyFrameSequence> SpdyFramer::CreateIterator(
     SpdyFramer* framer,
     std::unique_ptr<const SpdyFrameIR> frame_ir) {
-  std::unique_ptr<SpdyFrameSequence> result = nullptr;
   switch (frame_ir->frame_type()) {
     case SpdyFrameType::HEADERS: {
-      result = SpdyMakeUnique<SpdyHeaderFrameIterator>(
+      return SpdyMakeUnique<SpdyHeaderFrameIterator>(
           framer, SpdyWrapUnique(
                       static_cast<const SpdyHeadersIR*>(frame_ir.release())));
-      break;
     }
     case SpdyFrameType::PUSH_PROMISE: {
-      result = SpdyMakeUnique<SpdyPushPromiseFrameIterator>(
+      return SpdyMakeUnique<SpdyPushPromiseFrameIterator>(
           framer, SpdyWrapUnique(static_cast<const SpdyPushPromiseIR*>(
                       frame_ir.release())));
-      break;
     }
     case SpdyFrameType::DATA: {
       DVLOG(1) << "Serialize a stream end DATA frame for VTL";
       // FALLTHROUGH_INTENDED
     }
     default: {
-      result =
-          SpdyMakeUnique<SpdyControlFrameIterator>(framer, std::move(frame_ir));
+      return SpdyMakeUnique<SpdyControlFrameIterator>(framer,
+                                                      std::move(frame_ir));
     }
   }
-  return result;
 }
 
 void SpdyFramer::SerializeDataBuilderHelper(const SpdyDataIR& data_ir,