[Backport] Fix QuicIntervalDeque::Iterator::operator+=

The code was referring to a member which didn't exist. This was uncovered by a
recent Clang change [1] which made the compiler lookup these names at template
parse time rather than instantiation time.

 1. llvm/llvm-project#90152

Upstream-Status: Backport [google/quiche@c1af894]
Change-Id: I50bc7df75698a699365aa9752de9c0a9b0b0591f
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/564494
Reviewed-by: Peter Varga <[email protected]>
(cherry picked from commit 502a476)
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/586337
Reviewed-by: Qt Cherry-pick Bot <[email protected]>

Author: QUICHE team

chromium/net/third_party/quiche/src/quiche/quic/core/quic_interval_deque.h

@@ -198,12 +198,12 @@ class QUIC_NO_EXPORT QuicIntervalDeque {
     Iterator operator+(difference_type amount) const {
       Iterator copy = *this;
       copy.index_ += amount;
-      QUICHE_DCHECK(copy.index_ < copy.deque_->size());
+      QUICHE_DCHECK(copy.index_ < copy.deque_->Size());
       return copy;
     }
     Iterator& operator+=(difference_type amount) {
       index_ += amount;
-      QUICHE_DCHECK(index_ < deque_->size());
+      QUICHE_DCHECK(index_ < deque_->Size());
       return *this;
     }
     difference_type operator-(const Iterator& rhs) const {