Revert of IndexedDB: Don't timeout read-only transactions (https://codereview.chromium.org/180163010/)

Reason for revert:
Break Chromium Memory on Linux ASan+LSan Tests (2)

http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%2BLSan%20Tests%20%282%29/builds/65/steps/content_unittests/logs/NoTimeoutReadOnly

Original issue's description:
> IndexedDB: Don't timeout read-only transactions
> 
> Chrome introduced a transaction timeout to deal with potentially wedged
> renderers (e.g. JS execution halted, etc) failing to complete transactions,
> leaving the browser's transaction queue in a bad state. This was done
> for all transactions, but since read-only transactions don't hold up
> the queue it's safe to ignore them, which can reduce false-positives.
> 
> BUG=339229
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=254846

TBR=dgrogan@chromium.org,cmumford@chromium.org,jsbell@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=339229

Review URL: https://codereview.chromium.org/185403019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254868 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254868