[Tracing] Remove fields from AllocationContext

[Tracing] Remove fields from AllocationContext

These fields will return later on in the form of a trait set as proposed
in the Task Traits proposal. The |AllocationContextTracker| will not
keep track of general-purpose fields.

BUG=524631
Committed: https://crrev.com/2983eaac91b9edbd693b6955bde26e76741879d3
Cr-Commit-Position: refs/heads/master@{#357095}

[Ruud van Asseldonk, 2015-10-30 11:10:34]

ruuda@google.com changed reviewers:
+ primiano@chromium.org

[Ruud van Asseldonk, 2015-10-30 11:10:34]

We still need to do a more thorough cleanup of this file, but this is a start.

[Primiano Tucci (use gerrit), 2015-10-30 11:13:42]

lgtm

[Ruud van Asseldonk, 2015-10-30 14:03:50]

The CQ bit was checked by ruuda@google.com

[Ruud van Asseldonk, 2015-10-30 14:03:51]

The patchset sent to the CQ was uploaded after l-g-t-m from
primiano@chromium.org
Link to the patchset: https://codereview.chromium.org/1427953002/#ps20001
(title: "Add initializers to test to make MSVC happy")

[commit-bot: I haz the power, 2015-10-30 14:07:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1427953002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1427953002/20001

[commit-bot: I haz the power, 2015-10-30 14:14:15]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-30 14:15:11]

Patchset 2 (id:??) landed as
https://crrev.com/2983eaac91b9edbd693b6955bde26e76741879d3
Cr-Commit-Position: refs/heads/master@{#357095}