Free temporary GPU and memory resources held by inactive or hidden 2D canvases

Source/core/html/HTMLCanvasElement.h

Index: Source/core/html/HTMLCanvasElement.h
diff --git a/Source/core/html/HTMLCanvasElement.h b/Source/core/html/HTMLCanvasElement.h
index fa7ad1e8e8e6f016872a5483695b3220ad395423..e40c94e62956ee538e349971fefb7a065a50788a 100644
--- a/Source/core/html/HTMLCanvasElement.h
+++ b/Source/core/html/HTMLCanvasElement.h
@@ -31,6 +31,7 @@
 #include "core/html/HTMLElement.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntSize.h"
+#include "platform/graphics/Canvas2DLayerBridge.h"
 #include "wtf/Forward.h"
 
 #define DefaultInterpolationQuality InterpolationMedium
@@ -57,7 +58,7 @@ public:
     virtual void canvasDestroyed(HTMLCanvasElement*) = 0;
 };
 
-class HTMLCanvasElement FINAL : public HTMLElement {
+class HTMLCanvasElement FINAL : public HTMLElement, public Canvas2DLayerBridgeClient {
 public:
     static PassRefPtr<HTMLCanvasElement> create(Document&);
     virtual ~HTMLCanvasElement();
@@ -125,6 +126,9 @@ public:
 
     InsertionNotificationRequest insertedInto(ContainerNode*) OVERRIDE;
 
+    // Canvas2DLayerBridgeClient implementation
+    virtual bool hidden() const OVERRIDE { return document().hidden(); }

[eseidel, 2013/12/19 02:56:32]

Why do these individual elements know if they're hidden or not?

Shouldn't we just be signing up for some sort of "left the viewport" or "page
visibility chagned" notifications by things which care and then telling them via
some event/callback?

+
 private:
     explicit HTMLCanvasElement(Document&);