[DOM] When failing to create a channel and an image request, make sure to set

the image blocking status appropriately.

This is the same status as we do for known no-data protocols and ensures we
treat these two cases the same.

dom/base/nsImageLoadingContent.cpp

@@ -932,8 +932,12 @@ nsImageLoadingContent::LoadImage(nsIURI* aNewURI,
     MOZ_ASSERT(!req, "Shouldn't have non-null request here");
     // If we don't have a current URI, we might as well store this URI so people
     // know what we tried (and failed) to load.
-    if (!mCurrentRequest)
+    if (!mCurrentRequest) {
       mCurrentURI = aNewURI;
+      if (mImageBlockingStatus == nsIContentPolicy::ACCEPT) {
+        mImageBlockingStatus = nsIContentPolicy::REJECT_REQUEST;
+      }
+    }
 
     FireEvent(NS_LITERAL_STRING("error"));
     FireEvent(NS_LITERAL_STRING("loadend"));

layout/reftests/image/reftest.list

@@ -126,3 +126,5 @@ fuzzy(1,1) == image-orientation-background.html?90&flip      image-orientation-r
 
 == image-resize-percent-height.html image-resize-ref.html
 == image-resize-percent-width.html image-resize-ref.html
+
+== unknown-protocol.html unknown-protocol-ref.html

layout/reftests/image/unknown-protocol-ref.html

@@ -0,0 +1 @@
+<img src="mailto://foo">

layout/reftests/image/unknown-protocol.html

@@ -0,0 +1 @@
+<img src="foobar://baz">