IntersectionObserver: notify when root or target is removed.

third_party/WebKit/Source/core/dom/IntersectionObserver.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
index 9b02dfaa69334d0293ec18ec095d601aa672d549..2204a46cf6920570d223359aa1f560aa4dca399d 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserver.cpp
@@ -194,8 +194,6 @@ void IntersectionObserver::unobserve(Element* target)
 
 void IntersectionObserver::computeIntersectionObservations()
 {
-    if (!m_root || !m_root->inShadowIncludingDocument())

[ojan, 2016/04/15 18:19:08]

Moving this makes me a bit sad because it means we potentially do a lot of work
for an observer whose root is not in the tree, but I see why this patch needs
it. I think it's fine though. If we see code in the wild doing this, we can
optimize it (e.g. only do this work the first time the root is removed from the
tree instead of each frame).

-        return;
     Document* callbackDocument = toDocument(m_callback->getExecutionContext());
     if (!callbackDocument)
         return;