Remove ReceivedPostMessageFromNonDescendant UMA

Obtained desired data.

Bug: 841572, 891053
Change-Id: Ib81d8fb1ad0dc6df8437fe16264c249b60a5ae30
Reviewed-on: https://chromium-review.googlesource.com/c/1257856Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596116}

content/browser/frame_host/cross_process_frame_connector.cc

@@ -556,16 +556,6 @@ void CrossProcessFrameConnector::MaybeLogCrash(CrashVisibility visibility) {
 
   // Actually log the UMA.
   UMA_HISTOGRAM_ENUMERATION("Stability.ChildFrameCrash.Visibility", visibility);
-
-  if (visibility == CrashVisibility::kShownAfterCrashing) {
-    auto* rfh = frame_proxy_in_parent_renderer_->frame_tree_node()
-                    ->current_frame_host();
-    if (rfh->GetParent() && rfh->is_local_root()) {
-      UMA_HISTOGRAM_BOOLEAN(
-          "RenderFrameHostImpl.ReceivedPostMessageFromNonDescendant",
-          rfh->received_post_message_from_non_descendant());
-    }
-  }
 }
 
 bool CrossProcessFrameConnector::IsVisible() {

content/browser/frame_host/render_frame_host_impl.h

@@ -766,14 +766,6 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // for unload handler processing.
   void SetSubframeUnloadTimeoutForTesting(const base::TimeDelta& timeout);
 
-  bool received_post_message_from_non_descendant() const {
-    return received_post_message_from_non_descendant_;
-  }
-
-  void did_receive_post_message_from_non_descendant() {
-    received_post_message_from_non_descendant_ = true;
-  }
-
   // Returns the list of NavigationEntry ids corresponding to NavigationRequests
   // waiting to commit in this RenderFrameHost.
   std::set<int> GetNavigationEntryIdsPendingCommit();
@@ -1437,12 +1429,6 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // relevant NavigationEntry.
   int nav_entry_id_;
 
-  // Tracks if a frame has been influenced by post message from
-  // non-descendant frames. Useful for determining if silently reloading a
-  // crashed frame is safe. Post messages from descendants to not matter for
-  // this decision since they will be reloaded as well.
-  bool received_post_message_from_non_descendant_ = false;
-
   // Used to swap out or shut down this RFH when the unload event is taking too
   // long to execute, depending on the number of active frames in the
   // SiteInstance.  May be null in tests.

content/browser/frame_host/render_frame_proxy_host.cc

@@ -381,11 +381,6 @@ void RenderFrameProxyHost::OnRouteMessageEvent(
             ->SynchronizeVisualPropertiesIgnoringPendingAck();
       }
 
-      if (!source_rfh->frame_tree_node()->IsDescendantOf(
-              target_rfh->frame_tree_node())) {
-        target_rfh->did_receive_post_message_from_non_descendant();
-      }
-
       // Ensure that we have a swapped-out RVH and proxy for the source frame
       // in the target SiteInstance. If it doesn't exist, create it on demand
       // and also create its opener chain, since that will also be accessible

tools/metrics/histograms/histograms.xml

@@ -85488,6 +85488,9 @@ uploading your change for review.
 
 <histogram name="RenderFrameHostImpl.ReceivedPostMessageFromNonDescendant"
     enum="BooleanReceived" expires_after="2018-10-30">
+  <obsolete>
+    Removed Oct 2018.
+  </obsolete>
   <owner>alexmos@chromium.org</owner>
   <owner>boliu@chromium.org</owner>
   <summary>