Merge "libbacktrace: Fix clang-tidy warning"

libbacktrace/include/backtrace/BacktraceMap.h

@@ -79,7 +79,7 @@ public:
       index_++;
       return *this;
     }
-    iterator& operator++(int increment) {
+    const iterator operator++(int increment) {
       index_ += increment;
       return *this;
     }
@@ -87,7 +87,7 @@ public:
       index_--;
       return *this;
     }
-    iterator& operator--(int decrement) {
+    const iterator operator--(int decrement) {
       index_ -= decrement;
       return *this;
     }