Revert of Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not ha…

Revert of Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not ha… (patchset #1 id:1 of https://codereview.chromium.org/554583003/)

Reason for revert:
It looks like the moto E perf bots are broken. This change looks like it makes sense so I'm reverting.

crbug.com/414267

Original issue's description:
> Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not have been created at this point.
>
> BUG=413481
>
> Committed: https://crrev.com/9bb65868ce3ac1e5aae3a844beacf62281c332b6
> Cr-Commit-Position: refs/heads/master@{#294703}

TBR=nduca@chromium.org,nednguyen@google.com,tonyg@chromium.org,chrishenry@google.com,wuhu@google.com
NOTREECHECKS=true
NOTRY=true
BUG=413481
Committed: https://crrev.com/5f712b7be45145522f183d683f11bfb243dd89e1
Cr-Commit-Position: refs/heads/master@{#294816}

[dsinclair, 2014-09-15 13:52:27]

Created Revert of Change PageTest.WillStartBrowser to depend on platform instead
of browser object as it would not ha…

[dsinclair, 2014-09-15 17:54:49]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/569333002/ by dsinclair@chromium.org.

The reason for reverting is: Reverting the revert. Bot still failed with this CL
reverted. Sorry for the noise..