Debugger: remove bogus assertion in BreakLocation constructor.

Debugger: remove bogus assertion in BreakLocation constructor.

Currently DebugInfo objects can be created independently from whether
the debugger is active. When tearing down the isolate, we would go
through DebugInfo objects and iterate through break locations,
causing this assertion to fail.

R=ulan@chromium.org
BUG=v8:4241
LOG=N

Committed: https://crrev.com/f283021f2dfb1daa0e271ac7d5b3676e39202553
Cr-Commit-Position: refs/heads/master@{#29286}

[ulan, 2015-06-25 09:46:53]

lgtm

s/independelty/independently/ in the description

[Yang, 2015-06-25 09:48:40]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-06-25 09:48:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1210813002/1

[commit-bot: I haz the power, 2015-06-25 10:43:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-25 10:43:54]

Patchset 1 (id:??) landed as
https://crrev.com/f283021f2dfb1daa0e271ac7d5b3676e39202553
Cr-Commit-Position: refs/heads/master@{#29286}