IndexedDB: Remove transaction timer, just post tasks

IndexedDB: Remove transaction timer, just post tasks

In the Blink implementation transactions used a timer to
keep to schedule asynchronous processing of tasks. This
was retained in the Chromium port, but with access to the
message loop we can post tasks instead.

Note that transactions still maintain an internal list of
tasks and all that is posted is a "process the queue" task.
Future changes may integrate the transaction task queue and
the message loop more tightly.

BUG=246629
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=210969

[jsbell, 2013-07-10 17:38:40]

alecflett@, dgrogan@ - please take a look?

[dgrogan, 2013-07-10 18:35:13]

lgtm

This is an attempt to handle a performance regression right?

"process_queue_" was a little confusing, like it was a queue of processes, but I
couldn't come up with anything markedly better. I was thinking along the lines
of will_process_queue_, should_process_queue_ but they don't seem exactly right.

[jsbell, 2013-07-10 18:41:15]

On 2013/07/10 18:35:13, dgrogan wrote:
> lgtm
> 
> This is an attempt to handle a performance regression right?

Yes (crbug.com/246629), but also general cleanup. i.e. I think this is a good
idea even if we didn't have a performance issue.

> "process_queue_" was a little confusing, like it was a queue of processes, but
I
> couldn't come up with anything markedly better. I was thinking along the lines
> of will_process_queue_, should_process_queue_ but they don't seem exactly
right.

I agree. I'd also been thinking of "process_task_queue_" but that has the same
issue. I'll change it to should_process_queue_.

[commit-bot: I haz the power, 2013-07-10 19:08:08]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jsbell@chromium.org/18612007/5001

[commit-bot: I haz the power, 2013-07-10 23:37:16]

Change committed as 210969