Add consistency AssertRenderFrameExists check for iframes

This CL adds a WebContentsObserver consistency check inside
WebContentsObserverConsistencyChecker::RenderFrameHostChanged to
make sure that for every subframe,
WebContentsObserver::RenderFrameCreated is dispatched before
WebContentsObserver::RenderFrameHostChanged.

Previous CL (https://crrev.com/c/2614467) modified the
way the RenderFrameCreated and RenderFrameHostChanged
WebContentObserver callbacks were dispatched in the case of
sub-frames, ensuring this consistency check.

BUG=1097143

Change-Id: I2564fffad342d0ebf4945166b829b1b6e1f57b3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2628968
Commit-Queue: Sreeja Kamishetty <sreejakshetty@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846119}

content/test/web_contents_observer_consistency_checker.cc

@@ -140,6 +140,13 @@ void WebContentsObserverConsistencyChecker::RenderFrameHostChanged(
   EnsureStableParentValue(new_host);
   if (new_host->GetParent()) {
     AssertRenderFrameExists(new_host->GetParent());
+    // RenderFrameCreated should be called before RenderFrameHostChanged for all
+    // the subframes except for Portals which do not have a live RenderFrame in
+    // the renderer process.
+    if (new_host->GetFrameOwnerElementType() !=
+        blink::mojom::FrameOwnerElementType::kPortal) {
+      AssertRenderFrameExists(new_host);
+    }
     CHECK(current_hosts_.count(GetRoutingPair(new_host->GetParent())))
         << "Parent of frame being committed must be current.";
   }