Image maps should work for images with alt content

Source/core/layout/HitTestResult.cpp

Index: Source/core/layout/HitTestResult.cpp
diff --git a/Source/core/layout/HitTestResult.cpp b/Source/core/layout/HitTestResult.cpp
index 67ff7574695ae358d378b24caf21c635c7a567a9..1b8e0352cc63c2d58a4668f3cad5cfdde35837d0 100644
--- a/Source/core/layout/HitTestResult.cpp
+++ b/Source/core/layout/HitTestResult.cpp
@@ -153,12 +153,36 @@ void HitTestResult::setToShadowHostIfInUserAgentShadowRoot()
     }
 }
 
+HTMLAreaElement* HitTestResult::imageAreaForImage()

[pdr., 2015/04/26 02:59:15]

Lets make this function const since it doesn't modify m_innerNode itself.
HTMLAreaElement* HitTestResult::imageAreaForImage() const

+{
+    HTMLImageElement* imageElement = nullptr;

[pdr., 2015/04/26 02:59:15]

Even though we check it all over, I don't think m_innerNode can be null here.
Can you assert that?
ASSERT(m_innerNode);

+    if (isHTMLImageElement(innerNode()))
+        imageElement = toHTMLImageElement(innerNode());
+    else if (isHTMLImageElement(innerNode()->shadowHost()))

[pdr., 2015/04/26 02:59:15]

I think we need to limit this to user agent shadow hosts. For performance we may
want to check isInShadowTree too.

WDYT of the following?
if (isHTMLImageElement(m_innerNode)) {
    imageElement = toHTMLImageElement(innerNode());
} else if (m_innerNode->isInShadowTree()) {
    ShadowRoot* containingShadowRoot = m_innerNode->containingShadowRoot();
    if (containingShadowRoot->type() == ShadowRoot::UserAgentShadowRoot) {
        if (isHTMLImageElement(m_innerNode->shadowHost()))
            imageElement = toHTMLImageElement(m_innerNode->shadowHost());
    }
}

+        imageElement = toHTMLImageElement(innerNode()->shadowHost());
+
+    if (!imageElement)
+        return nullptr;
+
+    LayoutBox* box = toLayoutBox(layoutObject());

[pdr., 2015/04/26 02:59:15]

Nit: this can be moved inside the map conditional below.

+    LayoutRect contentBox = box->contentBoxRect();
+    float scaleFactor = 1 / box->style()->effectiveZoom();
+    LayoutPoint location = localPoint();
+    location.scale(scaleFactor, scaleFactor);
+
+    if (HTMLMapElement* map = imageElement->treeScope().getImageMap(imageElement->fastGetAttribute(usemapAttr)))
+        return map->areaForPoint(location, contentBox.size());
+    return nullptr;
+}
+
 void HitTestResult::setInnerNode(Node* n)
 {
     m_innerPossiblyPseudoNode = n;
     if (n && n->isPseudoElement())
         n = toPseudoElement(n)->findAssociatedNode();
     m_innerNode = n;
+    if (HTMLAreaElement* area = imageAreaForImage())
+        m_innerNode = area;
 }
 
 void HitTestResult::setURLElement(Element* n)