Move GetDocument method from WebFrame to WebLocalFrame.

chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc

Index: chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc
diff --git a/chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc b/chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc
index 4e1ef0bebc328bcec260c2b09dab9d8b99dad7b5..641017996263c13a34e2616c6f54876b1963c8f3 100644
--- a/chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc
+++ b/chrome/renderer/safe_browsing/phishing_dom_feature_extractor.cc
@@ -390,8 +390,10 @@ blink::WebDocument PhishingDOMFeatureExtractor::GetNextDocument() {
   // Advance to the next frame that contains a document, with no wrapping.
   if (frame) {
     for (frame = frame->TraverseNext(); frame; frame = frame->TraverseNext()) {
-      if (!frame->GetDocument().IsNull()) {
-        return frame->GetDocument();
+      // TODO(dcheng): Verify if the WebDocument::IsNull check is really needed.
+      if (frame->IsWebLocalFrame() &&
+          !frame->ToWebLocalFrame()->GetDocument().IsNull()) {
+        return frame->ToWebLocalFrame()->GetDocument();
       }
     }
   } else {