Fix UB in the integer overflow check in Layer::Layer()
Note that this doesn't fix a data race reported in issue 345251

BUG=345251
R=danakj@chromium.org

Review URL: https://codereview.chromium.org/175033002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252672 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252672
Merge https://codereview.chromium.org/168133002 to trunk

> Fix one last problem with merge of 251380
>
> This was supposed to use the list of installed extensions, not just
> enabled ones.
>
> > Don't disable extensions immediately if verification is out of date
> >
> > If the install verification signature we have stored in our prefs is
> > older than the install time of an extension, we don't want to
> > immediately disable it. Instead, we want to do another server request to
> > update our signature, and then disable if appropriate.
> >
> > BUG=342165
> > R=finnur@chromium.org
> >
> > Review URL: https://codereview.chromium.org/160313002

BUG=345499

TBR=asargent@chromium.org

Review URL: https://codereview.chromium.org/174933003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252673 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252673