Replace DumpWithoutCrashing by CHECK for srcdoc CommitNavigation()

about:srcdoc document is always loaded inside an iframe and is
same-SiteInstance with its parent.

This is checked in CommitNavigation.

As a precautionary measure, this initially landed as a
DumpWithoutCrashing() to avoid hurting canary/dev/beta users if those
check were violated. It was planned to remove the DumpWithoutCrashing
for M79 if there was no reported DumpWithoutCrashing.

There are none of them:
https://crash.corp.google.com/browse?q=product_name%3D%22Chrome%22+AND+STRPOS%28expanded_custom_data.ChromeCrashProto.magic_signature_1.name%2C+%27CommitNavigation%27%29+%3E+0+AND+expanded_custom_data.ChromeCrashProto.magic_signature_1.name%3D%27content%3A%3ARenderFrameHostImpl%3A%3ACommitNavigation%27+AND+product.Version%3E%3D%2778.0.3904.63%27&stbtiq=&reportid=70db5bbe497238ba&index=9#4

Bug: None
Change-Id: Iee51ddcb31fd3a7b1b7155c02f726e24c160f31c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1913401
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715115}

content/browser/frame_host/render_frame_host_impl.cc

@@ -5237,26 +5237,14 @@ void RenderFrameHostImpl::CommitNavigation(
 
   bool is_srcdoc = common_params->url.IsAboutSrcdoc();
   if (is_srcdoc) {
-    if (frame_tree_node_->IsMainFrame()) {
-      // Main frame srcdoc navigation are meaningless. They are blocked whenever
-      // a navigation attempt is made.
-      //
-      // TODO(arthursonzogni): Replace DumpWithoutCrashing by a CHECK on M79 if
-      // it is never reached.
-      NOTREACHED();
-      base::debug::DumpWithoutCrashing();
-    } else {
-      // An about:srcdoc document is always same SiteInstance with its parent.
-      // Otherwise, it won't be able to load. The parent's document contains the
-      // iframe and its srcdoc attribute.
-      //
-      // TODO(arthursonzogni): Replace DumpWithoutCrashing by a CHECK on M80 if
-      // it is never reached.
-      if (GetSiteInstance() != parent_->GetSiteInstance()) {
-        NOTREACHED();
-        base::debug::DumpWithoutCrashing();
-      }
-    }
+    // Main frame srcdoc navigation are meaningless. They are blocked whenever a
+    // navigation attempt is made. It shouldn't reach CommitNavigation.
+    CHECK(!frame_tree_node_->IsMainFrame());
+
+    // An about:srcdoc document is always same SiteInstance with its parent.
+    // Otherwise, it won't be able to load. The parent's document contains the
+    // iframe and its srcdoc attribute.
+    CHECK_EQ(GetSiteInstance(), parent_->GetSiteInstance());
   }
 
   // If this is an attempt to commit a URL in an incompatible process, capture a