leak_detector: call transform() with back_inserter

components/metrics/leak_detector/leak_detector.cc

Index: components/metrics/leak_detector/leak_detector.cc
diff --git a/components/metrics/leak_detector/leak_detector.cc b/components/metrics/leak_detector/leak_detector.cc
index 5bf61b5b92b2d41b69a49a4f49dd26b93c1fe649..518047e994a940d20b5b6a4fc2bb59049ad6dd08 100644
--- a/components/metrics/leak_detector/leak_detector.cc
+++ b/components/metrics/leak_detector/leak_detector.cc
@@ -268,8 +268,10 @@ void LeakDetector::AllocHook(const void* ptr, size_t size) {
 
       // Pass leak reports to observers.
       std::vector<MemoryLeakReportProto> leak_report_protos;
+      leak_report_protos.reserve(leak_reports.size());
       std::transform(leak_reports.begin(), leak_reports.end(),
-                     leak_report_protos.begin(), &ConvertLeakReportToProto);
+                     std::back_inserter(leak_report_protos),
+                     &ConvertLeakReportToProto);
       detector->NotifyObservers(leak_report_protos);
     }
   }