[whatwg] history.back()

[Darin Fisher]

In WebKit, history.back() is currently implemented asynchronously.

However, it was not always this way.  Previously, if the back navigation
corresponded to a hash change, then the back navigation would complete
synchronously.  If the back navigation corresponded to a different document,
then it would be completed asynchronously.

The HTML5 spec currently calls for the old behavior of WebKit, which happens
to match the behavior of Gecko.  Because the spec is written this way, there
is movement in WebKit to change WebKit back.

IE however appears to implement history.back() asynchronously in all cases
just like newer versions of WebKit.

I actually think this is a better behavior to spec for a couple reasons:

1)  It allows for history.back() to behave consistently regardless of the
type of navigation.
2)  It allows for the back/forward list to be decoupled from the main thread
of the rendering engine.

This last point is quite relevant to Chrome since we store the back/forward
list in a separate process.  We do this since items in the back/forward list
may actually need to be rendered using different WebKit processes.
 (Navigating in the location bar is a hint that we can spawn a new process.)

We could copy the entire back/forward list to each process and replicate
state, but that seems excessive.  Instead, simply matching the
history.back() behavior of IE avoids the need to do so.

>From a web compat perspective, it seems wise to match the behavior of IE.
 It also has other benefits.

Can we change the spec?

-Darin
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