Revert 268232 "Refactor MetricsStateManager class out of Metrics..."

Revert 268232 "Refactor MetricsStateManager class out of Metrics..."

Failed 'sizes' check: chrome-si (static initializers) incremented.

> Refactor MetricsStateManager class out of MetricsService.
> 
> The new class is responsible for managing various MetricsService state prefs,
> such as client id, low entropy source and the UMA opt-in state, as well as the
> cloned install detector.
> 
> Also, moves IsMetricsReportingEnabled() from chrome_browser_main.cc to
> the new class as well as changing a couple MetricsService browser tests
> to instead be unit tests of the new class.
> 
> BUG=368413
> 
> Review URL: https://codereview.chromium.org/256143006

TBR=asvitkine@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=268246

[miu, 2014-05-05 19:38:45]

Build that failed:
http://build.chromium.org/p/chromium/buildstatus?builder=Linux%20x64&number=6...

The culprit seems to be:  +bool MetricsStateManager::instance_exists_ = false;

[miu, 2014-05-05 19:38:52]

Committed patchset #1 manually as r268246 (tree was closed).