[tracing] Fixing freelist snapshot of blink gc dump provider.

[tracing] Fixing freelist snapshot of blink gc dump provider.

m_firstUnsweptPage after makeConsistentForMutator() is always null. So,
this cannot be checked during freelist snapshot. The check is not
useful here since there cannot be page dump when there is no freelist.
Hence this is removed.

BUG=490087
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197807

[ssid, 2015-06-25 06:22:27]

ssid@chromium.org changed reviewers:
+ haraken@chromium.org

[haraken, 2015-06-25 06:25:48]

LGTM

[ssid, 2015-06-25 06:31:28]

ssid@chromium.org changed reviewers:
+ primiano@chromium.org

[ssid, 2015-06-25 06:31:32]

The CQ bit was checked by ssid@chromium.org

[ssid, 2015-06-25 06:47:13]

The CQ bit was unchecked by ssid@chromium.org

[ssid, 2015-06-25 09:21:03]

The CQ bit was checked by ssid@chromium.org

[commit-bot: I haz the power, 2015-06-25 09:21:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1206203002/1

[commit-bot: I haz the power, 2015-06-25 09:25:19]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197807