heap: Resolve -Wshadow warning in allocation-observer.cc

Bug: v8:12244, v8:12245
Change-Id: Id6b9e0a3986fb04c1a949b26ecf20da652ddd097
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3181537
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77045}

src/heap/allocation-observer.cc

@@ -4,6 +4,9 @@
 
 #include "src/heap/allocation-observer.h"
 
+#include <algorithm>
+#include <cstdint>
+
 #include "src/heap/heap.h"
 #include "src/heap/spaces.h"
 
@@ -58,15 +61,16 @@ void AllocationCounter::RemoveAllocationObserver(AllocationObserver* observer) {
   if (observers_.size() == 0) {
     current_counter_ = next_counter_ = 0;
   } else {
-    size_t step_size = 0;
-
-    for (AllocationObserverCounter& observer : observers_) {
-      size_t left_in_step = observer.next_counter_ - current_counter_;
-      DCHECK_GT(left_in_step, 0);
-      step_size = step_size ? std::min(step_size, left_in_step) : left_in_step;
-    }
-
-    next_counter_ = current_counter_ + step_size;
+    // There's at least one observer.
+    const size_t min_next_counter =
+        std::min_element(observers_.begin(), observers_.end(),
+                         [](const auto& a, const auto& b) {
+                           return a.next_counter_ < b.next_counter_;
+                         })
+            ->next_counter_;
+    DCHECK_GT(min_next_counter, current_counter_);
+    const size_t min_step_size = min_next_counter - current_counter_;
+    next_counter_ = current_counter_ + min_step_size;
   }
 }