Make multipart image documents work again.

Source/core/fetch/Resource.h

Index: Source/core/fetch/Resource.h
diff --git a/Source/core/fetch/Resource.h b/Source/core/fetch/Resource.h
index 58340fd9b3733b006e2141bfbccce67610c7ac88..be5421de50c2d21f55f3c51d82b659b175b8d21f 100644
--- a/Source/core/fetch/Resource.h
+++ b/Source/core/fetch/Resource.h
@@ -170,6 +170,7 @@ public:
             && type() != Raw
             && type() != TextTrack;
     }
+    bool canBeMultipart() const { return type() == Image || type() == MainResource; }

[Mike West, 2015/05/28 05:51:54]

This seems unclear; we don't support multipart for _any_ MainResource, do we?
What happens if we try to load a non-image multipart document?

[Nate Chapin, 2015/05/28 17:44:24]

We fail. I was hoping to convey some level of ambiguity with "can" in the
function name. Maybe leave this inlined with a comment in
ResourceLoader::didReceiveResponse() is clearer?

 
     // Computes the status of an object after loading.
     // Updates the expire date on the cache entry file