Fix IPCChannelMojoErrorTest.SendFailWithPendingMessages

Fix IPCChannelMojoErrorTest.SendFailWithPendingMessages

The test has been broken since MojoBootstrap was introduced.
The change makes it impossible to inject failure from the ChannelMojo
subclass.

This change uses large data as pending message to trigger failure,
instead of overloading IPC::ChannelMojo functions.

R=viettrungluu@chromium.org
BUG=417439
Committed: https://crrev.com/be6c4ccb1377a0ffd5b31ef9b56b70474a126833
Cr-Commit-Position: refs/heads/master@{#296565}

[Hajime Morrita, 2014-09-24 22:19:48]

Trung: Could you take a look? A trivial test fix.

[viettrungluu, 2014-09-24 22:28:20]

lgtm

[Hajime Morrita, 2014-09-24 22:29:32]

The CQ bit was checked by morrita@chromium.org

[commit-bot: I haz the power, 2014-09-24 22:30:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/598093006/1

[commit-bot: I haz the power, 2014-09-24 23:38:50]

Committed patchset #1 (id:1) as 8927f20831098339766965528b93db13778be8fa

[commit-bot: I haz the power, 2014-09-24 23:47:07]

Patchset 1 (id:??) landed as
https://crrev.com/be6c4ccb1377a0ffd5b31ef9b56b70474a126833
Cr-Commit-Position: refs/heads/master@{#296565}