[SPv2] Adds pre-computed paint property context to PaintLayer.

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 5d1baa9407f29d25a01ef613fe06c6d213a6fbc6..45838aaf9f958197b2af27d207f2231b1baebd3a 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -57,6 +57,7 @@
 #include "core/paint/PaintLayerStackingNode.h"
 #include "core/paint/PaintLayerStackingNodeIterator.h"
 #include "platform/graphics/CompositingReasons.h"
+#include "platform/graphics/paint/PaintChunkProperties.h"
 #include "public/platform/WebBlendMode.h"
 #include "wtf/Allocator.h"
 #include "wtf/OwnPtr.h"
@@ -130,6 +131,11 @@ struct PaintLayerRareData {
 
     // The accumulated subpixel offset of a composited layer's composited bounds compared to absolute coordinates.
     LayoutSize subpixelAccumulation;
+
+    struct CachedSPv2PaintParameters {
+        LayoutPoint paintOffset;
+        PaintChunkProperties properties;
+    } cachedSPv2PaintParameters;

[pdr., 2016/02/02 06:18:20]

Is this data actually rare or is it just on raredata temporarily?

Can you add a short comment above CachedSPv2PaintParameters explaining what it's
for?

We can name this something better than CachedSPv2PaintParameters, but I don't
understand this patch well enough to make a suggestion. If this is just for
overflow clip, maybe something like CachedSPv2OverflowClipPaintState?

[trchen, 2016/02/02 21:48:53]

It will be no longer rare once SPv2 ships. :)
Acknowledged.
Yea... The variable name is too generic. Having the code name SPv2 in there
isn't good either. However it is not exclusive for overflow either, as I'm
planning to include paint context for fixed-pos descendants in the future (for
background-attachment:fixed). Does CachedLayerPaintPropertyContext sound better?

 };
 
 // PaintLayer is an old object that handles lots of unrelated operations.
@@ -679,6 +685,9 @@ public:
     }
     void clearClipRectsCache() const { m_clipRectsCache.clear(); }
 
+    const PaintLayerRareData::CachedSPv2PaintParameters& cachedSPv2PaintParameters() const { ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled()); ASSERT(m_rareData); return m_rareData->cachedSPv2PaintParameters; }

[pdr., 2016/02/02 06:18:20]

WDYT about some lifecycle asserts here?

For the accessor, something like ASSERT(DocumentLifecycle::InPaint)?

For the setter, something like
ASSERT(DocumentLifecycle::InUpdatePaintProperties)?

[trchen, 2016/02/02 21:48:53]

Acknowledged. Hey, fantastic idea!

+    PaintLayerRareData::CachedSPv2PaintParameters& accessCachedSPv2PaintParameters() { ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled()); return ensureRareData().cachedSPv2PaintParameters; }
+
 private:
     // Bounding box in the coordinates of this layer.
     LayoutRect logicalBoundingBox() const;