Improve QUIC flow-control commentary and variable-names.

net/quic/core/quic_flow_controller.cc

Index: net/quic/core/quic_flow_controller.cc
diff --git a/net/quic/core/quic_flow_controller.cc b/net/quic/core/quic_flow_controller.cc
index 1c27276a1cd89dd8102ea980248480261d5663b7..715d938c44e106d5146a4017644e28bf50f0ecff 100644
--- a/net/quic/core/quic_flow_controller.cc
+++ b/net/quic/core/quic_flow_controller.cc
@@ -250,9 +250,12 @@ bool QuicFlowController::UpdateSendWindowOffset(
                 << " current offset: " << send_window_offset_
                 << " bytes_sent: " << bytes_sent_;
 
-  const bool blocked = IsBlocked();
+  // The flow is now unblocked but could have also been unblocked
+  // before.  Return true iff this update caused a change from blocked
+  // to unblocked.
+  const bool was_previously_blocked = IsBlocked();
   send_window_offset_ = new_send_window_offset;
-  return blocked;
+  return was_previously_blocked;
 }
 
 void QuicFlowController::EnsureWindowAtLeast(QuicByteCount window_size) {