[Backport] Fix base::IDMap::Iterator::operator=

It was referring to non-existing members of Iterator.

Presumably this wasn't noticed because the compiler was doing the name
lookup at instantiation time and this function was never instantiated,
but a recent Clang change [1] uncovered it.

 1. llvm/llvm-project#90152

Upstream-Status: Backport [https://chromium-review.googlesource.com/c/chromium/src/+/5512719]
Bug: 338536260
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5512719
Auto-Submit: Hans Wennborg <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1296463}
Pick-to: 118-based
Change-Id: I2192aab954f58b6b555822dea6801fddcb99f8f0
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/586000
Reviewed-by: Peter Varga <[email protected]>

Author: zmodem

chromium/base/containers/id_map.h

@@ -178,8 +178,8 @@ class IDMap final {
     }
 
     const Iterator& operator=(const Iterator& iter) {
-      map_ = iter.map;
-      iter_ = iter.iter;
+      map_ = iter.map_;
+      iter_ = iter.iter_;
       Init();
       return *this;
     }