content: Fix problem with implementation of MergeIntoFreeList.

content: Fix problem with implementation of MergeIntoFreeList.

When merging span with previous span, the start of span should
only be removed if the start doesn't also represent the end of
span.

BUG=429416
TEST=content_unittests --gtest_filter=DiscardableSharedMemoryHeapTest.MergeSingleBlockSpan

Committed: https://crrev.com/6349d624ac8853f0eb106510835fb0cd17850534
Cr-Commit-Position: refs/heads/master@{#317516}

[reveman, 2015-02-21 18:50:00]

reveman@chromium.org changed reviewers:
+ avi@chromium.org

[Avi (use Gerrit), 2015-02-21 20:27:00]

lgtm

ok

[reveman, 2015-02-21 20:29:29]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2015-02-21 20:30:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/947743002/1

[commit-bot: I haz the power, 2015-02-21 20:38:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-21 20:39:49]

Patchset 1 (id:??) landed as
https://crrev.com/6349d624ac8853f0eb106510835fb0cd17850534
Cr-Commit-Position: refs/heads/master@{#317516}