[tracing] Clean up the MemoryInfra API surface (3/3)

[tracing] Clean up the MemoryInfra API surface (3/3)

This patch simplifies the API surface of MemoryInfra switching
attribute names from std::string to char*.

The main goal is to make the dumping fast and predictable memory-wise.
There is no point allowing the attribute names to be arbitrary strings
(read non static "quoted" char* ptrs). That has the only effect of
causing loads of copies and std::string ctors / dtors.

BUG=495628, 480500
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196952

[Primiano Tucci (use gerrit), 2015-06-11 00:48:27]

primiano@chromium.org changed reviewers:
+ pdr@chromium.org, rbyers@chromium.org

[Primiano Tucci (use gerrit), 2015-06-11 00:48:28]

Follows from crrev.com/1173253002, see my message there.

[Rick Byers, 2015-06-11 01:38:50]

lgtm

[Primiano Tucci (use gerrit), 2015-06-11 12:45:24]

The CQ bit was checked by primiano@chromium.org

[commit-bot: I haz the power, 2015-06-11 12:45:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1176223002/1

[commit-bot: I haz the power, 2015-06-11 14:57:08]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196952