Improved the reporting of background color information.

third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp

 /*
 * Copyright (C) 2008 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 821 matching lines @@
     if (!node->isElementNode())
         return nullAtom;
     return toElement(node)->getAttribute(accesskeyAttr);
 }
 
 RGBA32 AXLayoutObject::backgroundColor() const
 {
     if (!getLayoutObject())
         return AXNodeObject::backgroundColor();
 
-    const ComputedStyle* style = getLayoutObject()->style();
-    if (!style || !style->hasBackground())
-        return AXNodeObject::backgroundColor();
+    Color blendedColor = Color::transparent;
+    for (LayoutObject* layoutObject = getLayoutObject(); layoutObject;

[aboxhall, 2016/05/24 17:06:34]

Unfortunately, walking up the parent chain often isn't sufficient because of
absolute positioning.

I wrote code for this in devtools:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

I wonder if we can reuse that here, somehow?

+        layoutObject = layoutObject->parent()) {
+        const ComputedStyle* style = layoutObject->style();
+        if (!style || !style->hasBackground())
+            continue;
 
-    Color color = style->visitedDependentColor(CSSPropertyBackgroundColor);
-    return color.rgb();
+        Color currentColor = style->visitedDependentColor(CSSPropertyBackgroundColor);
+        blendedColor = blendedColor.blend(currentColor);
+        // Continue blending until we get opacity to more than 50%
+        if (blendedColor.alpha() > 128)

[aboxhall, 2016/05/24 17:06:34]

I share Dominic's concern here: for example, 51% red over blue appears purple,
not blue.

+            break;
+    }
+
+    // If we still have a low level of opacity, blend in the document base color.
+    if (blendedColor.alpha() <= 128) {
+        FrameView* view = documentFrameView();
+        if (view) {
+            Color documentBaseColor = view->baseBackgroundColor();
+            blendedColor = blendedColor.blend(documentBaseColor);
+        }
+    }
+
+    return blendedColor.rgb();
 }
 
 RGBA32 AXLayoutObject::color() const
 {
     if (!getLayoutObject() || isColorWell())
         return AXNodeObject::color();
 
     const ComputedStyle* style = getLayoutObject()->style();
     if (!style)
         return AXNodeObject::color();
@@ skipping 813 matching lines @@
 
 Document* AXLayoutObject::getDocument() const
 {
     if (!getLayoutObject())
         return nullptr;
     return &getLayoutObject()->document();
 }
 
 FrameView* AXLayoutObject::documentFrameView() const
 {
-    if (!m_layoutObject)
-        return 0;
+    if (!getLayoutObject())
+        return nullptr;
 
     // this is the LayoutObject's Document's LocalFrame's FrameView
-    return m_layoutObject->document().view();
+    return getLayoutObject()->document().view();
 }
 
 Element* AXLayoutObject::anchorElement() const
 {
     if (!m_layoutObject)
         return 0;
 
     AXObjectCacheImpl& cache = axObjectCache();
     LayoutObject* currLayoutObject;
 
@@ skipping 781 matching lines @@
         if (label && label->layoutObject()) {
             LayoutRect labelRect = axObjectCache().getOrCreate(label)->elementRect();
             result.unite(labelRect);
         }
     }
 
     return result;
 }
 
 } // namespace blink