Fix and improve Map::CurrentMapForDeprecatedInternal().

Fix and improve Map::CurrentMapForDeprecatedInternal().

Inline relevant bits from Map::FindUpdatedMap() and Map::IsMoreGeneralThan()
into Map::CurrentMapForDeprecatedInternal() to fix issues introduced
with field type tracking, avoid the useless second pass over the transition
tree, and finally make it easier to understand what this method actually
does.

TEST=mjsunit/regress/regress-365172-2
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=20997

Committed: https://code.google.com/p/v8/source/detail?r=21010

[Benedikt Meurer, 2014-04-28 05:54:25]

PTAL

[Sven Panne, 2014-04-28 06:28:30]

lgtm

[Benedikt Meurer, 2014-04-28 06:31:29]

Committed patchset #1 manually as r20997 (presubmit successful).

[Benedikt Meurer, 2014-04-28 11:09:15]

Committed patchset #1 manually as r21010 (presubmit successful).

[Toon Verwaest, 2014-05-06 13:39:59]

This CL definitely does not LGTM. Especially given that the actually committed
change is ~2-3x larger than what is indicated here. What's the point of inlining
all this code!? Abstractions are there for a reason, please don't throw them
away just because it looks more convenient for the single change you are doing.

[Benedikt Meurer, 2014-05-07 06:35:55]

There was no abstraction. FindUpdatedMap() was basically wrong for both call
sites, that's why we had to walk the path again to see if we could actually use
the updated map. So for these two callers, FindUpdatedMap() was not the right
choice (anymore, it may have been different in the past), and since there was no
other caller for FindUpdatedMap(), it was dead code and thereby removed.

[Toon Verwaest, 2014-05-07 07:50:22]

Then why does it look like now there are around 200 lines of extra code where 4
function calls used to be? E.g DescriptorArray::Merge?

[Benedikt Meurer, 2014-05-07 08:05:21]

There are only ~40 additional lines of "extra code" in this CL, and they express
exactly what Map::CurrentMapForDeprecatedInternal() is supposed to do. That's
way more readable (and certainly more correct) than using FindUpdatedMap() and
IsMoreGeneralThan().