Reland: Optimizes IndexedDB's DeleteDatabase when no db exists

Reland: Optimizes IndexedDB's DeleteDatabase when no db exists

When deleting the non existing database in a origin with no existing
backing store, then in DeleteDatabse(), early exiting before
OpenBackingStore, so that it wont results in multiple transaction as
earlier.

Original patch by: payal.pandey

This was reverted (see crrev.com/1071553002) when it appeared to make
a test flaky, but the test continues to flake (now tracked as
crbug.com/505609) so let's try relanding.

BUG=460236
Committed: https://crrev.com/4cbc8f1b383fb8145056295176912d53030a98b0
Cr-Commit-Position: refs/heads/master@{#336796}

[jsbell, 2015-06-29 22:19:13]

jsbell@chromium.org changed reviewers:
+ cmumford@chromium.org

[jsbell, 2015-06-29 22:19:14]

cmumford@ - PTAL?

[cmumford, 2015-06-30 16:38:49]

The CQ bit was checked by cmumford@chromium.org

[cmumford, 2015-06-30 16:38:52]

The CQ bit was unchecked by cmumford@chromium.org

[cmumford, 2015-06-30 16:39:13]

The CQ bit was checked by cmumford@chromium.org

[cmumford, 2015-06-30 16:39:13]

lgtm

Hit commit button

[commit-bot: I haz the power, 2015-06-30 16:40:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216573008/1

[commit-bot: I haz the power, 2015-06-30 16:46:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-30 16:47:42]

Patchset 1 (id:??) landed as
https://crrev.com/4cbc8f1b383fb8145056295176912d53030a98b0
Cr-Commit-Position: refs/heads/master@{#336796}

[vkuzkokov, 2015-07-02 16:18:10]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1225513002/ by vkuzkokov@chromium.org.

The reason for reverting is: Some bots still flaky. See crbug.com/506467.