Make multipart image documents work again.

Source/core/html/ImageDocument.cpp

Index: Source/core/html/ImageDocument.cpp
diff --git a/Source/core/html/ImageDocument.cpp b/Source/core/html/ImageDocument.cpp
index 8fe7336858781632fcda90fb1a3d172791207de5..2413c2da116165f056c5e870d7bf49e334865067 100644
--- a/Source/core/html/ImageDocument.cpp
+++ b/Source/core/html/ImageDocument.cpp
@@ -136,6 +136,10 @@ void ImageDocumentParser::appendBytes(const char* data, size_t length)
         RELEASE_ASSERT(length <= std::numeric_limits<unsigned>::max());
         document()->cachedImage()->appendData(data, length);
     }
+
+    if (!document())
+        return;
+
     // Make sure the image layoutObject gets created because we need the layoutObject
     // to read the aspect ratio. See crbug.com/320244
     document()->updateLayoutTreeIfNeeded();
@@ -164,7 +168,8 @@ void ImageDocumentParser::finish()
         document()->imageUpdated();
     }
 
-    document()->finishedParsing();
+    if (document())
+        document()->finishedParsing();
 }
 
 // --------
@@ -186,7 +191,7 @@ PassRefPtrWillBeRawPtr<DocumentParser> ImageDocument::createParser()
     return ImageDocumentParser::create(this);
 }
 
-void ImageDocument::createDocumentStructure()
+void ImageDocument::createDocumentStructure(bool loadingMultipartContent)
 {
     RefPtrWillBeRawPtr<HTMLHtmlElement> rootElement = HTMLHtmlElement::create(*this);
     appendChild(rootElement);
@@ -194,6 +199,13 @@ void ImageDocument::createDocumentStructure()
 
     if (frame())
         frame()->loader().dispatchDocumentElementAvailable();
+    // Normally, ImageDocument creates an HTMLImageElement that doesn't actually load
+    // anything, and the ImageDocument routes the main resource data into the HTMLImageElement's
+    // ImageResource. However, the main resource pipeline doesn't know how to handle multipart content.
+    // For multipart content, we instead stop streaming data through the main resource and re-request
+    // the data directly.
+    if (loadingMultipartContent)
+        loader()->stopLoading();
 
     RefPtrWillBeRawPtr<HTMLHeadElement> head = HTMLHeadElement::create(*this);
     RefPtrWillBeRawPtr<HTMLMetaElement> meta = HTMLMetaElement::create(*this);
@@ -206,7 +218,10 @@ void ImageDocument::createDocumentStructure()
 
     m_imageElement = HTMLImageElement::create(*this);
     m_imageElement->setAttribute(styleAttr, "-webkit-user-select: none");
-    m_imageElement->setLoadingImageDocument();
+    // If the image is multipart, we neglect to mention to the HTMLImageElement that it's in an
+    // ImageDocument, so that it requests the image normally.
+    if (!loadingMultipartContent)
+        m_imageElement->setLoadingImageDocument();
     m_imageElement->setSrc(url().string());
     body->appendChild(m_imageElement.get());
 
@@ -221,6 +236,8 @@ void ImageDocument::createDocumentStructure()
 
     rootElement->appendChild(head);
     rootElement->appendChild(body);
+    if (loadingMultipartContent)
+        finishedParsing();
 }
 
 float ImageDocument::scale() const
@@ -387,10 +404,11 @@ void ImageDocument::windowSizeChanged(ScaleType type)
 
 ImageResource* ImageDocument::cachedImage()
 {
+    bool loadingMultipartContent = loader() && loader()->loadingMultipartContent();
     if (!m_imageElement)
-        createDocumentStructure();
+        createDocumentStructure(loadingMultipartContent);
 
-    return m_imageElement->cachedImage();
+    return loadingMultipartContent ? nullptr : m_imageElement->cachedImage();
 }
 
 bool ImageDocument::shouldShrinkToFit() const