Reland PaintChunk::id

third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h

Index: third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h b/third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h
index e3dc42b883a6c58de348012f02eefe01a20808d0..f076a8c606334772f77382089761c041fede8fad 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h
@@ -63,7 +63,11 @@ public:
 
     PaintInvalidationReason getPaintInvalidationReason() const { return m_cacheGenerationOrInvalidationReason.getPaintInvalidationReason(); }
 
+    // A client is considered "just created" if its display items have never been committed.
+    bool isJustCreated() const { return m_cacheGenerationOrInvalidationReason.isJustCreated(); }
+
 private:
+    friend class FakeDisplayItemClient;
     friend class PaintController;
 
     // Holds a unique cache generation id of DisplayItemClients and PaintControllers,
@@ -81,12 +85,16 @@ private:
     // only. The client will be treated as invalid on other paint controllers regardless if
     // it's validly cached by these paint controllers. The situation is very rare (about 0.07%
     // clients were painted on multiple paint controllers) so the performance penalty is trivial.
-    class CacheGenerationOrInvalidationReason {
+    class PLATFORM_EXPORT CacheGenerationOrInvalidationReason {
         DISALLOW_NEW();
     public:
-        CacheGenerationOrInvalidationReason() { invalidate(); }
+        CacheGenerationOrInvalidationReason() : m_value(kJustCreated) { }
 
-        void invalidate(PaintInvalidationReason reason = PaintInvalidationFull) { m_value = static_cast<ValueType>(reason); }
+        void invalidate(PaintInvalidationReason reason = PaintInvalidationFull)
+        {
+            if (m_value != kJustCreated)
+                m_value = static_cast<ValueType>(reason);
+        }
 
         static CacheGenerationOrInvalidationReason next()
         {
@@ -103,14 +111,17 @@ private:
 
         PaintInvalidationReason getPaintInvalidationReason() const
         {
-            return m_value < kFirstValidGeneration ? static_cast<PaintInvalidationReason>(m_value) : PaintInvalidationNone;
+            return m_value < kJustCreated ? static_cast<PaintInvalidationReason>(m_value) : PaintInvalidationNone;
         }
 
+        bool isJustCreated() const { return m_value == kJustCreated; }
+
     private:
         typedef uint32_t ValueType;
         explicit CacheGenerationOrInvalidationReason(ValueType value) : m_value(value) { }
 
-        static const ValueType kFirstValidGeneration = static_cast<ValueType>(PaintInvalidationReasonMax) + 1;
+        static const ValueType kJustCreated = static_cast<ValueType>(PaintInvalidationReasonMax) + 1;
+        static const ValueType kFirstValidGeneration = static_cast<ValueType>(PaintInvalidationReasonMax) + 2;
         static ValueType s_nextGeneration;
         ValueType m_value;
     };