components: Add out-of-line copy ctors for complex classes.

components/security_interstitials/core/metrics_helper.h

Index: components/security_interstitials/core/metrics_helper.h
diff --git a/components/security_interstitials/core/metrics_helper.h b/components/security_interstitials/core/metrics_helper.h
index 17b493d303e3102d0008f190a00aef34b0005a56..aab9d10cb1f53eba04ef56e2cb5c83391ca335ff 100644
--- a/components/security_interstitials/core/metrics_helper.h
+++ b/components/security_interstitials/core/metrics_helper.h
@@ -67,6 +67,7 @@ class MetricsHelper {
   // The rappor preferences can be left blank if rappor_service is not set.
   struct ReportDetails {
     ReportDetails();
+    ReportDetails(const ReportDetails& other);
     std::string metric_prefix;
     std::string extra_suffix;
     std::string rappor_prefix;