Fix partial painting with render pipeline throttling

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 7ff3eef3fabf9fcbf135b808dc4f78bcae459381..cb195caf5deb2f3ab9c1f2bc4312355e8551d175 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -4,6 +4,7 @@
 
 #include "core/paint/PaintLayerPainter.h"
 
+#include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
@@ -80,10 +81,6 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayer(GraphicsContext& co
     if (shouldSuppressPaintingLayer(&m_paintLayer))
         return FullyPainted;
 
-    // TODO(skyostil): Unify this early-out logic with subsequence caching.
-    if (m_paintLayer.layoutObject()->isLayoutPart() && toLayoutPart(m_paintLayer.layoutObject())->isThrottledFrameView())
-        return FullyPainted;
-
     // If this layer is totally invisible then there is nothing to paint.
     if (!m_paintLayer.layoutObject()->opacity() && !m_paintLayer.layoutObject()->hasBackdropFilter())
         return FullyPainted;
@@ -269,9 +266,13 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerContents(GraphicsCon
     if (paintFlags & PaintLayerPaintingRootBackgroundOnly && !m_paintLayer.layoutObject()->isLayoutView() && !m_paintLayer.layoutObject()->isDocumentElement())
         return result;
 
-    // TODO(skyostil): Unify this early-out logic with subsequence caching.
-    if (m_paintLayer.layoutObject()->isLayoutPart() && toLayoutPart(m_paintLayer.layoutObject())->isThrottledFrameView())
-        return FullyPainted;
+    if (m_paintLayer.layoutObject()->isLayoutView() && toLayoutView(m_paintLayer.layoutObject())->frameView()->shouldThrottleRendering()) {
+        // Make sure we re-record any cached subsequence when this layer becomes
+        // unthrottled again.
+        result = MayBeClippedByPaintDirtyRect;
+        m_paintLayer.setPreviousPaintResult(result);
+        return result;

[chrishtr, 2016/01/20 17:08:11]

I think you need to call m_paintLayer.setPreviousPaintResult(result) before
returning here. Does that fix your current bug?

[Sami, 2016/01/20 18:06:42]

Hmm, isn't that what I'm doing on line 273 or did I miss something?-)

[Sami, 2016/01/20 18:10:09]

And to be clear the other part of the bugfix is this line here:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

[Xianzhu, 2016/01/20 18:31:12]

I think we need to clear m_paintLayer's other previousXXX states to avoid them
happening to be the same as the new ones once the FrameView becomes
non-throttled.

[Sami, 2016/01/20 18:49:31]

Good point. Looks like it should be sufficient to reset previousPaintDirtyRect?
(or instead ensure needsRepaint is set if we decide to do that instead.)

[Xianzhu, 2016/01/20 18:51:03]

needsRepaint should be suffice.

+    }
 
     // Ensure our lists are up-to-date.
     m_paintLayer.stackingNode()->updateLayerListsIfNeeded();