Let clientCacheIsValid count cacheable display item only

This is just a consolidation. No observed bug.

Non-cacheable display items might use different early return policy
during painting and make clientCacheIsValid true even if there is no
cached cacheable display items.

Review URL: https://codereview.chromium.org/1323253002

git-svn-id: svn://svn.chromium.org/blink/trunk@201692 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/graphics/paint/DisplayItemList.cpp

@@ -458,13 +458,14 @@ void DisplayItemList::updateValidlyCachedClientsIfNeeded() const
     m_validlyCachedClients.clear();
     m_validlyCachedClientsDirty = false;
 
-    DisplayItemClient lastClient = nullptr;
+    DisplayItemClient lastAddedClient = nullptr;
     for (const DisplayItem& displayItem : m_currentDisplayItems) {
-        if (displayItem.client() == lastClient)
+        if (displayItem.client() == lastAddedClient)
             continue;
-        lastClient = displayItem.client();
-        if (!displayItem.skippedCache())
-            m_validlyCachedClients.add(lastClient);
+        if (displayItem.isCacheable()) {
+            lastAddedClient = displayItem.client();
+            m_validlyCachedClients.add(lastAddedClient);
+        }
     }
 }