[content] Add DumpWithoutCrashing to WebContents::FromRenderFrameHost.

We are considering returning nullptr for
WebContents::FromRenderFrameHost is the RenderFrameHost is not the
current one.

This patch adds a behind-the-flag option to start generating crash dumps
to allow us to find the places which need to be fixed before that.

R=alexmos@chromium.org
BUG=1059903

Change-Id: Iaca4f30dfef1d6b6e03194a990bebf3e1649b39c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2093228Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748950}

content/browser/web_contents/web_contents_impl.cc

@@ -193,6 +193,11 @@ namespace {
 const int kMinimumDelayBetweenLoadingUpdatesMS = 100;
 const char kDotGoogleDotCom[] = ".google.com";
 
+// TODO(crbug.com/1059903): Clean up after the initial investigation.
+constexpr base::Feature kCheckWebContentsAccessFromNonCurrentFrame{
+    "CheckWebContentsAccessFromNonCurrentFrame",
+    base::FEATURE_DISABLED_BY_DEFAULT};
+
 base::LazyInstance<std::vector<
     WebContentsImpl::FriendWrapper::CreatedCallback>>::DestructorAtExit
     g_created_callbacks = LAZY_INSTANCE_INITIALIZER;
@@ -368,6 +373,11 @@ WebContents* WebContents::FromRenderViewHost(RenderViewHost* rvh) {
 WebContents* WebContents::FromRenderFrameHost(RenderFrameHost* rfh) {
   if (!rfh)
     return nullptr;
+  if (!rfh->IsCurrent() && base::FeatureList::IsEnabled(
+                               kCheckWebContentsAccessFromNonCurrentFrame)) {
+    // TODO(crbug.com/1059903): return nullptr here eventually.
+    base::debug::DumpWithoutCrashing();
+  }
   return static_cast<RenderFrameHostImpl*>(rfh)->delegate()->GetAsWebContents();
 }