Introduce Range::dispose() for prompt detachment from owner Document.

Source/web/WebLocalFrameImpl.cpp

Index: Source/web/WebLocalFrameImpl.cpp
diff --git a/Source/web/WebLocalFrameImpl.cpp b/Source/web/WebLocalFrameImpl.cpp
index 5e2b49ed4ad94f60b53136cab1ed99bba2dc580d..342e1d0dc5dc27821fc42045d5adaa4f574dd29c 100644
--- a/Source/web/WebLocalFrameImpl.cpp
+++ b/Source/web/WebLocalFrameImpl.cpp
@@ -256,6 +256,8 @@ static void frameContentAsPlainText(size_t maxChars, LocalFrame* frame, StringBu
 
     // Select the document body.
     RefPtrWillBeRawPtr<Range> range(document->createRange());
+    ScopedDisposal<Range> disposeScope(range);
+
     TrackExceptionState exceptionState;
     range->selectNodeContents(document->body(), exceptionState);

[yosin_UTC9, 2015/09/11 01:22:27]

We can use |EphemeralRange| here.

// ClusterFuzz can changes document w/o body.
if (!document->body())
    return;
const EphemeralRange range = rangeOfContents(*document->body());

[sof, 2015/09/11 06:32:12]

Nice; done, I think.