Revert of Attempting to resolve a race condition with PowerMonitor

Revert of Attempting to resolve a race condition with PowerMonitor (https://codereview.chromium.org/179923006/)

Reason for revert:
Failing interactive_ui_tests dbg:

http://build.chromium.org/p/chromium.win/builders/Interactive%20Tests%20(dbg)/builds/47083/steps/interactive_ui_tests/logs/stdio

Original issue's description:
> Attempting to resolve a race condition with PowerMonitor.
> 
> ThreadSanitizer caught multiple instances where PowerMonitor::Get or PowerMonitor::Add/RemoveObserver were being called concurrently with the PowerMonitor constructor in the main thread. These functions access a process-global PowerMontior instance (g_power_monitor), which was not thread safe.
> 
> This change adds locks around PowerMonitor creation and deletion, and forces Add/RemoveObserver to be called in a threadsafe manner. It also removes the need to call PowerMonitor::Get.
> 
> BUG=268924
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=262018

TBR=mattm@chromium.org,jyasskin@chromium.org,kbr@chromium.org,bradnelson@chromium.org,brettw@chromium.org,bradchen@chromium.org,willchan@chromium.org,jam@chromium.org,jochen@chromium.org,timurrrr@chromium.org,glider@chromium.org,acolwell@chromium.org,scherkus@chromium.org,bajones@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=268924
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=262026

[scottmg, 2014-04-05 18:55:26]

Created Revert of Attempting to resolve a race condition with PowerMonitor

[commit-bot: I haz the power, 2014-04-05 18:55:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/scottmg@chromium.org/226263008/1

[commit-bot: I haz the power, 2014-04-05 18:56:00]

Change committed as 262026

[Nico, 2014-04-05 19:03:50]

(FWIW, browser_tests got pretty red on windows after this too:
http://build.chromium.org/p/chromium.win/buildstatus?builder=Win7%20Tests%20%...
)