Cleanup: Remove if (!CurrentlyOn()) PostTask() pattern in EmbeddedWorkerInstance

Cleanup: Remove if (!CurrentlyOn()) PostTask() pattern in EmbeddedWorkerInstance

Per discussion on chromium-dev (https://groups.google.com/a/chromium.org/d/msg/chromium-dev/uWGNk-hVlGc/M92wu3izhGEJ)
I'm removing following code pattern from non-thread-safe code.

void DoSomething() {
    if (!BrowserThread::CurrentlyOn(BrowserThread::UI)) {
        BrowserThread::PostTask(BrowserThread::UI,
            FROM_HERE,
            base::Bind(DoSomething);
        return;
    }
    ...
}

This pattern is handy, but this could mislead readers to think that the method can be called from any threads, while it's not.

(We use similar patterns a lot in ServiceWorkerContextWrapper, but the class is intended to be thread-safe so I think the usage there should be ok)

BUG=N/A
TEST=existing tests

Committed: https://crrev.com/6f6121790f0f4f5f97fc3b125b261f4e5efd8334
Cr-Commit-Position: refs/heads/master@{#310447}

[kinuko, 2015-01-07 08:37:22]

Patchset #1 (id:1) has been deleted

[kinuko, 2015-01-07 10:34:50]

kinuko@chromium.org changed reviewers:
+ horo@chromium.org

[kinuko, 2015-01-07 10:35:59]

Cleanup only, PTL

[horo, 2015-01-07 14:47:33]

lgtm

[kinuko, 2015-01-08 02:04:10]

The CQ bit was checked by kinuko@chromium.org

[commit-bot: I haz the power, 2015-01-08 02:05:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/796393005/20001

[commit-bot: I haz the power, 2015-01-08 03:02:38]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-01-08 03:03:19]

Patchset 1 (id:??) landed as
https://crrev.com/6f6121790f0f4f5f97fc3b125b261f4e5efd8334
Cr-Commit-Position: refs/heads/master@{#310447}