Allow nested state restorers in DrawingBuffer

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
index 0bc3e68c9e63fd5f00422ac52097bf33dca34ad2..9acbaf3b2f3649d022e3d7930fa425bcb4e7bb3e 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -270,6 +270,8 @@ class PLATFORM_EXPORT DrawingBuffer
 
    private:
     RefPtr<DrawingBuffer> m_drawingBuffer;
+    // The previous state restorer, in case restorers are nested.
+    ScopedStateRestorer* m_previousStateRestorer = nullptr;
     bool m_clearStateDirty = false;
     bool m_pixelPackAlignmentDirty = false;
     bool m_textureBindingDirty = false;