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

Source/core/html/HTMLCanvasElement.cpp

Index: Source/core/html/HTMLCanvasElement.cpp
diff --git a/Source/core/html/HTMLCanvasElement.cpp b/Source/core/html/HTMLCanvasElement.cpp
index ae520f32f8e825c698f310b478cd4769e155f020..4261c16be2d9766a3c6298130bc45f207be91457 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -71,6 +71,7 @@ static const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 
 HTMLCanvasElement::HTMLCanvasElement(Document& document)
     : HTMLElement(canvasTag, document)
+    , DocumentVisibilityObserver(document)
     , m_size(DefaultWidth, DefaultHeight)
     , m_rendererIsCanvas(false)
     , m_ignoreReset(false)
@@ -571,4 +572,26 @@ AffineTransform HTMLCanvasElement::baseTransform() const
     return m_imageBuffer->baseTransform();
 }
 
+void HTMLCanvasElement::didChangeVisibilityState(PageVisibilityState visibility)
+{
+    if (hasImageBuffer()) {
+        bool hidden = visibility != PageVisibilityStateVisible;
+        if (hidden) {
+            clearCopiedImage();
+            if (is3D()) {
+                m_imageBuffer.clear();
+            }
+        }
+        if (hasImageBuffer()) {
+            m_imageBuffer->setIsHidden(hidden);
+        }
+    }
+}
+
+void HTMLCanvasElement::didMoveToNewDocument(Document& oldDocument)
+{
+    setObservedDocument(document());
+    HTMLElement::didMoveToNewDocument(oldDocument);
+}
+
 }