Get rid of AXComputedObjectAttributeCache

We added AXComputedObjectAttributeCache to WebKit because we wanted to
cache some expensive computations in the AX tree, but none of the other
WebKit ports wanted it.

A much simpler solution is to just store the cached value inside the
AXObject. To determine if the value is out of date, I added a
modification count that increments whenever there's a layout or DOM
mutation. We can reuse the same modification count for more cached
attributes.

BUG=425879

Review URL: https://codereview.chromium.org/670093002

git-svn-id: svn://svn.chromium.org/blink/trunk@184331 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/accessibility/AXObject.cpp

@@ -134,6 +134,8 @@ AXObject::AXObject()
     , m_role(UnknownRole)
     , m_lastKnownIsIgnoredValue(DefaultBehavior)
     , m_detached(false)
+    , m_lastModificationCount(-1)
+    , m_cachedIsIgnored(false)
 {
 }
 
@@ -247,30 +249,22 @@ bool AXObject::isClickable() const
 }
 
 bool AXObject::accessibilityIsIgnored() const
+{
+    updateCachedAttributeValuesIfNeeded();
+    return m_cachedIsIgnored;
+}
+
+void AXObject::updateCachedAttributeValuesIfNeeded() const
 {
     AXObjectCacheImpl* cache = axObjectCache();
     if (!cache)
-        return true;
-
-    AXComputedObjectAttributeCache* attributeCache = cache->computedObjectAttributeCache();
-    if (attributeCache) {
-        AXObjectInclusion ignored = attributeCache->getIgnored(axObjectID());
-        switch (ignored) {
-        case IgnoreObject:
-            return true;
-        case IncludeObject:
-            return false;
-        case DefaultBehavior:
-            break;
-        }
-    }
-
-    bool result = computeAccessibilityIsIgnored();
+        return;
 
-    if (attributeCache)
-        attributeCache->setIgnored(axObjectID(), result ? IgnoreObject : IncludeObject);
+    if (cache->modificationCount() == m_lastModificationCount)
+        return;
 
-    return result;
+    m_cachedIsIgnored = computeAccessibilityIsIgnored();
+    m_lastModificationCount = cache->modificationCount();
 }
 
 bool AXObject::accessibilityIsIgnoredByDefault() const

third_party/WebKit/Source/core/accessibility/AXObject.h

@@ -579,6 +579,14 @@ protected:
     unsigned getLengthForTextRange() const { return text().length(); }
 
     bool m_detached;
+
+private:
+    // The following cached attribute values (the ones starting with m_cached*)
+    // are only valid if m_lastModificationCount matches AXObjectCacheImpl::modificationCount().
+    mutable int m_lastModificationCount;
+    mutable bool m_cachedIsIgnored;
+
+    void updateCachedAttributeValuesIfNeeded() const;
 };
 
 #define DEFINE_AX_OBJECT_TYPE_CASTS(thisType, predicate) \

third_party/WebKit/Source/core/accessibility/AXObjectCacheImpl.cpp

@@ -88,34 +88,11 @@ AXObjectCache* AXObjectCache::create(Document& document)
     return new AXObjectCacheImpl(document);
 }
 
-AXObjectInclusion AXComputedObjectAttributeCache::getIgnored(AXID id) const
-{
-    HashMap<AXID, CachedAXObjectAttributes>::const_iterator it = m_idMapping.find(id);
-    return it != m_idMapping.end() ? it->value.ignored : DefaultBehavior;
-}
-
-void AXComputedObjectAttributeCache::setIgnored(AXID id, AXObjectInclusion inclusion)
-{
-    HashMap<AXID, CachedAXObjectAttributes>::iterator it = m_idMapping.find(id);
-    if (it != m_idMapping.end()) {
-        it->value.ignored = inclusion;
-    } else {
-        CachedAXObjectAttributes attributes;
-        attributes.ignored = inclusion;
-        m_idMapping.set(id, attributes);
-    }
-}
-
-void AXComputedObjectAttributeCache::clear()
-{
-    m_idMapping.clear();
-}
-
 AXObjectCacheImpl::AXObjectCacheImpl(Document& document)
     : m_document(document)
+    , m_modificationCount(0)
     , m_notificationPostTimer(this, &AXObjectCacheImpl::notificationPostTimerFired)
 {
-    m_computedObjectAttributeCache = AXComputedObjectAttributeCache::create();
 }
 
 AXObjectCacheImpl::~AXObjectCacheImpl()
@@ -758,7 +735,7 @@ void AXObjectCacheImpl::postNotification(RenderObject* renderer, AXNotification
     if (!renderer)
         return;
 
-    m_computedObjectAttributeCache->clear();
+    m_modificationCount++;
 
     // Get an accessibility object that already exists. One should not be created here
     // because a render update may be in progress and creating an AX object can re-trigger a layout
@@ -779,7 +756,7 @@ void AXObjectCacheImpl::postNotification(Node* node, AXNotification notification
     if (!node)
         return;
 
-    m_computedObjectAttributeCache->clear();
+    m_modificationCount++;
 
     // Get an accessibility object that already exists. One should not be created here
     // because a render update may be in progress and creating an AX object can re-trigger a layout
@@ -797,7 +774,7 @@ void AXObjectCacheImpl::postNotification(Node* node, AXNotification notification
 
 void AXObjectCacheImpl::postNotification(AXObject* object, Document* document, AXNotification notification, bool postToElement, PostType postType)
 {
-    m_computedObjectAttributeCache->clear();
+    m_modificationCount++;
 
     if (object && !postToElement)
         object = object->observableObject();
@@ -843,7 +820,7 @@ void AXObjectCacheImpl::handleScrollbarUpdate(FrameView* view)
 
     // We don't want to create a scroll view from this method, only update an existing one.
     if (AXObject* scrollViewObject = get(view)) {
-        m_computedObjectAttributeCache->clear();
+        m_modificationCount++;
         scrollViewObject->updateChildrenIfNecessary();
     }
 }
@@ -853,7 +830,7 @@ void AXObjectCacheImpl::handleLayoutComplete(RenderObject* renderer)
     if (!renderer)
         return;
 
-    m_computedObjectAttributeCache->clear();
+    m_modificationCount++;
 
     // Create the AXObject if it didn't yet exist - that's always safe at the end of a layout, and it
     // allows an AX notification to be sent when a page has its first layout, rather than when the
@@ -878,7 +855,7 @@ void AXObjectCacheImpl::handleAriaRoleChanged(Node* node)
 {
     if (AXObject* obj = getOrCreate(node)) {
         obj->updateAccessibilityRole();
-        m_computedObjectAttributeCache->clear();
+        m_modificationCount++;
         obj->notifyIfIgnoredValueChanged();
     }
 }

third_party/WebKit/Source/core/accessibility/AXObjectCacheImpl.h

@@ -52,27 +52,6 @@ struct TextMarkerData {
     EAffinity affinity;
 };
 
-class AXComputedObjectAttributeCache {
-public:
-    static PassOwnPtr<AXComputedObjectAttributeCache> create() { return adoptPtr(new AXComputedObjectAttributeCache()); }
-
-    AXObjectInclusion getIgnored(AXID) const;
-    void setIgnored(AXID, AXObjectInclusion);
-
-    void clear();
-
-private:
-    AXComputedObjectAttributeCache() { }
-
-    struct CachedAXObjectAttributes {
-        CachedAXObjectAttributes() : ignored(DefaultBehavior) { }
-
-        AXObjectInclusion ignored;
-    };
-
-    HashMap<AXID, CachedAXObjectAttributes> m_idMapping;
-};
-
 enum PostType { PostSynchronously, PostAsynchronously };
 
 // This class should only be used from inside the accessibility directory.
@@ -174,7 +153,9 @@ public:
 
     bool nodeHasRole(Node*, const AtomicString& role);
 
-    AXComputedObjectAttributeCache* computedObjectAttributeCache() { return m_computedObjectAttributeCache.get(); }
+    // Counts the number of times the document has been modified. Some attribute values are cached
+    // as long as the modification count hasn't changed.
+    int modificationCount() const { return m_modificationCount; }
 
     void postNotification(RenderObject*, AXNotification, bool postToElement, PostType = PostAsynchronously);
     void postNotification(Node*, AXNotification, bool postToElement, PostType = PostAsynchronously);
@@ -198,7 +179,7 @@ private:
     HashMap<Node*, AXID> m_nodeObjectMapping;
     HashMap<AbstractInlineTextBox*, AXID> m_inlineTextBoxObjectMapping;
     HashSet<Node*> m_textMarkerNodes;
-    OwnPtr<AXComputedObjectAttributeCache> m_computedObjectAttributeCache;
+    int m_modificationCount;
 
     HashSet<AXID> m_idsInUse;