This sounds very much like what 5ad4faa93d2554ffab7f72a992adbeffa8796f94 implemented. The "not in viewport" bit ought to be Image subclass agnostic. (Does PaintInvalidationDelayedFull cover that well enough?)

I think we can apply the same thing already done for LayoutBox and background-image
of LayoutBox that works for animated GIFs.

Animated GIF throttling works like this:

1. A timer fires from the image saying that the image has a new frame to draw
2. LayoutImage (or LayoutBox) hears that and invalidates paint on itself.
3. In the next document lifecycle, the Layout{Image,Box} paints itself. As part of
this it asks the image to paint itself into the display list.
4. When painting itself, BitmapImage::draw() will paint itself, then call
BitmapImpage::startAnimation() on itself. This sets off a timer to go back to step 1.

Our code short-circuits this cycle for animated GIFs by issuing a "delayed" paint
invalidation at step 2 when we notice that the GIF is not visible (by calling
LayoutBox::intersectsVisibleViewport). If that returns true, we upgrade to a non-delayed
invalidation for that frame, and otherwise issue an invalidation to be checked again
for paint invalidation in the next frame.

It appears that SVGImage uses the same pattern as BitmapImage, so therefore we can do the
same for SVG images. In fact, I'm not sure why it doesn't work already. Is the ImageResource not
returning maybeAnimated in invalidation in LayoutImage?

fs@ would you like to take a look?

Adding to backlog.

Looks like Image::maybeAnimated() isn't even overridden for SVGImage. Doing that should be easy enough since we already have essentially the same predicate already (from an old version of the same method even I think...)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bb03bc3127de97898e62323b12cd2997267cfd5a

commit bb03bc3127de97898e62323b12cd2997267cfd5a
Author: fs <fs@opera.com>
Date: Fri Mar 31 10:38:13 2017

Implement Image::maybeAnimated for SVGImage

This CL renames SVGImage::hasAnimations to maybeAnimated, overriding
the implementation from the base class (Image.) The old method matches
the new one in certainty of the reply, and allows SVGImages to be paused
when being scrolled out of view etc.

BUG= 706152 

Review-Url: https://codereview.chromium.org/2783133002
Cr-Commit-Position: refs/heads/master@{#461094}

[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-background-offscreen-expected.txt
[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-background-offscreen.html
[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-offscreen-expected.txt
[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-offscreen.html
[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-transformed-offscreen-expected.txt
[add] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/LayoutTests/paint/invalidation/svg/animated-svg-as-image-transformed-offscreen.html
[modify] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/Source/core/svg/graphics/SVGImage.cpp
[modify] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/Source/core/svg/graphics/SVGImage.h
[modify] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/Source/core/svg/graphics/SVGImageChromeClient.cpp
[modify] https://crrev.com/bb03bc3127de97898e62323b12cd2997267cfd5a/third_party/WebKit/Source/core/svg/graphics/SVGImageTest.cpp

I think all components should be there now.