[S.P.] Don't draw frames of animated images that are offscreen.

Source/core/layout/LayoutImage.cpp

Index: Source/core/layout/LayoutImage.cpp
diff --git a/Source/core/layout/LayoutImage.cpp b/Source/core/layout/LayoutImage.cpp
index 047eb6b8a95183bb4146c7c6b91b1f001c26e477..92e92d2ae409206b6c09447c5227012af0f99493 100644
--- a/Source/core/layout/LayoutImage.cpp
+++ b/Source/core/layout/LayoutImage.cpp
@@ -40,6 +40,7 @@
 #include "core/html/HTMLMapElement.h"
 #include "core/layout/HitTestResult.h"
 #include "core/layout/Layer.h"
+#include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/PaintInfo.h"
 #include "core/layout/TextRunConstructor.h"
@@ -176,6 +177,30 @@ void LayoutImage::invalidatePaintAndMarkForLayoutIfNeeded()
     contentChanged(ImageChanged);
 }
 
+bool LayoutImage::rectIntersectsVisibleViewport(const LayoutRect& localRect)
+{
+    LayoutRect rect = localRect;
+    LayoutView* layoutView = view();
+    while (layoutView->frame()->ownerLayoutObject())
+        layoutView = layoutView->frame()->ownerLayoutObject()->view();
+    mapRectToPaintInvalidationBacking(layoutView, rect, 0);
+    return rect.intersects(LayoutRect(layoutView->frameView()->visualViewportRect()));
+}
+
+PaintInvalidationReason LayoutImage::invalidatePaintIfNeeded(const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
+{
+    if (!RuntimeEnabledFeatures::slimmingPaintEnabled())
+        return LayoutReplaced::invalidatePaintIfNeeded(paintInvalidationState, paintInvalidationContainer);
+
+    if (!imageResource() || !imageResource()->image() || !imageResource()->image()->maybeAnimated()
+        || rectIntersectsVisibleViewport(visualOverflowRect())) {
+        return LayoutReplaced::invalidatePaintIfNeeded(paintInvalidationState, paintInvalidationContainer);
+    }
+
+    return PaintInvalidationDelayedFull;

[chrishtr, 2015/03/16 23:07:41]

Since this method overrides invalidatePaintIfNeeded, in the case where this line
is reached all the code in LayoutObject::invalidatePaintIfNeeded never runs.
This means that no paint invalidation rects are issued at all, leading to no
paint and no raster.

[chrishtr, 2015/03/17 23:55:56]

Correct. That is the intention of the CL.

+}
+
+
 void LayoutImage::notifyFinished(Resource* newImage)
 {
     if (!m_imageResource)