Handle LocalFrame being nestedly detached by subframe.

Source/core/loader/FrameLoader.cpp

Index: Source/core/loader/FrameLoader.cpp
diff --git a/Source/core/loader/FrameLoader.cpp b/Source/core/loader/FrameLoader.cpp
index d30381816e394784adbab83d4f7480a317701995..0cc4801b3fc93292853195e6554b456b4bbb59eb 100644
--- a/Source/core/loader/FrameLoader.cpp
+++ b/Source/core/loader/FrameLoader.cpp
@@ -479,7 +479,8 @@ void FrameLoader::finishedParsing()
     // Null-checking the FrameView indicates whether or not we're in the destructor.
     RefPtrWillBeRawPtr<LocalFrame> protect(m_frame->view() ? m_frame.get() : nullptr);
 
-    m_progressTracker->finishedParsing();
+    if (m_progressTracker)

[Nate Chapin, 2015/08/17 17:01:58]

Is there any work that needs to be done in the frame-already-detached case? Can
we early-exit at the top of the function instead?

[sof, 2015/08/18 05:24:13]

It won't do any work before the detach check just below, so you could insert
another one at the top here.

This is related to #2 -- it seems preferable to head off repeated LocalFrame
detaches at the frame level, rather than at the auxiliary FrameLoader.

+        m_progressTracker->finishedParsing();
 
     if (client())
         client()->dispatchDidFinishDocumentLoad(m_documentLoader->isCommittedButEmpty());