Revert of Reduce plugin_metrics_provider_ usage in MetricsService

Revert of Reduce plugin_metrics_provider_ usage in MetricsService (https://codereview.chromium.org/308433004/)

Reason for revert:
This CL seems to cause bot failure on CI:
http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%281%29/builds/2745

Original issue's description:
> Reduce plugin_metrics_provider_ usage in MetricsService
> 
> This CL eliminates MetricsService's call to
> PluginMetricsProvider::RecordPluginChanges (replaced by a new API on
> MetricsProvider). It additionally adds a
> MetricsServicesManager::OnPluginLoadingError() API and has the plugin observer
> call that API rather than calling MetricsService directly. This change will
> enable easily moving MetricsService::LogPluginLoadingError() to
> ChromeMetricsServiceClient once the latter is the class that keeps a weak
> pointer to the plugin metrics provider.
> 
> BUG=375776
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274403

TBR=asvitkine@chromium.org,isherman@chromium.org,jochen@chromium.org,blundell@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=375776
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274418

[tzik, 2014-06-03 04:37:37]

Created Revert of Reduce plugin_metrics_provider_ usage in MetricsService

[commit-bot: I haz the power, 2014-06-03 04:38:11]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tzik@chromium.org/314583002/1

[commit-bot: I haz the power, 2014-06-03 04:40:25]

Change committed as 274418