Add Java wrapper for RenderFrameHost

This patch adds a Java wrapper for RenderFrameHost. It also adds a
getMainFrame method to WebContents.

This will be useful for Payment Request which needs to know
the exact (sub)frame issued the payment request.

BUG=620173
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2681933002
Cr-Original-Commit-Position: refs/heads/master@{#455635}
Committed: https://chromium.googlesource.com/chromium/src/+/67dd9f2795389cc3776481ff07740984b2389f43
Review-Url: https://codereview.chromium.org/2681933002
Cr-Commit-Position: refs/heads/master@{#456152}
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 8647047..dfde98b 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -3586,6 +3586,13 @@
       web_contents, allowed_per_prefs, origin, resource_url);
 }
 
+#if defined(OS_ANDROID)
+base::android::ScopedJavaLocalRef<jobject>
+WebContentsImpl::GetJavaRenderFrameHostDelegate() {
+  return GetJavaWebContents();
+}
+#endif
+
 void WebContentsImpl::OnDidDisplayContentWithCertificateErrors(
     RenderFrameHostImpl* source,
     const GURL& url) {