Update OnCommit to return ObservePolicy.

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index 0a1bf48d2475c23ef94aaf2c9fa5c120d7301306..1ca66e37badf183e35d83311e16ae78205437a41 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -33,6 +33,19 @@
 DEFINE_WEB_CONTENTS_USER_DATA_KEY(
     page_load_metrics::MetricsWebContentsObserver);
 
+// This macro invokes the specified method on each observer, passing the
+// variable length arguments as the method's arguments, and removes the observer
+// from the list of observers if the given method returns STOP_OBSERVING.
+#define INVOKE_AND_PRUNE_OBSERVERS(observers, Method, ...)    \
+  for (auto it = observers.begin(); it != observers.end();) { \
+    if ((*it)->Method(__VA_ARGS__) ==                         \
+        PageLoadMetricsObserver::STOP_OBSERVING) {            \
+      it = observers.erase(it);                               \
+    } else {                                                  \
+      ++it;                                                   \
+    }                                                         \
+  }
+
 namespace page_load_metrics {
 
 namespace internal {
@@ -442,9 +455,8 @@ void PageLoadTracker::Commit(content::NavigationHandle* navigation_handle) {
   // Some transitions (like CLIENT_REDIRECT) are only known at commit time.
   page_transition_ = navigation_handle->GetPageTransition();
   user_gesture_ = navigation_handle->HasUserGesture();
-  for (const auto& observer : observers_) {
-    observer->OnCommit(navigation_handle);
-  }
+
+  INVOKE_AND_PRUNE_OBSERVERS(observers_, OnCommit, navigation_handle);
   LogAbortChainHistograms(navigation_handle);
 }
 
@@ -475,14 +487,8 @@ void PageLoadTracker::FlushMetricsOnAppEnterBackground() {
   }
 
   const PageLoadExtraInfo info = ComputePageLoadExtraInfo();
-  for (auto it = observers_.begin(); it != observers_.end();) {
-    if ((*it)->FlushMetricsOnAppEnterBackground(timing_, info) ==
-        PageLoadMetricsObserver::STOP_OBSERVING) {
-      it = observers_.erase(it);
-    } else {
-      ++it;
-    }
-  }
+  INVOKE_AND_PRUNE_OBSERVERS(observers_, FlushMetricsOnAppEnterBackground,
+                             timing_, info);
 }
 
 void PageLoadTracker::NotifyClientRedirectTo(