Revert of Handle RenderProcessHostImpl::SetBackgrounded on Windows

Revert of Handle RenderProcessHostImpl::SetBackgrounded on Windows (patchset #4 id:60001 of https://codereview.chromium.org/926663002/)

Reason for revert:
This patch set re-enabled ChromeRenderProcessHostTest.Backgrounding, which is now failing on XP bots.

Example logs:
https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/35740/steps/browser_tests%20on%20Windows-XP-SP3/logs/ChromeRenderProcessHostTest.Backgrounding
https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/35740/steps/browser_tests%20on%20Windows-XP-SP3/logs/ChromeRenderProcessHostTest.Backgrounding



ChromeRenderProcessHostTest.Backgrounding (run #1):
[ RUN      ] ChromeRenderProcessHostTest.Backgrounding
[2904:3280:0219/073309:WARNING:data_reduction_proxy_settings.cc(365)] SPDY proxy OFF at startup
[2904:2900:0219/073309:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073309:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073310:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:2900:0219/073311:WARNING:raw_channel.cc(210)] Shutting down RawChannel with write buffer nonempty
[2904:3280:0219/073311:WARNING:pref_notifier_impl.cc(27)] pref observer found at shutdown printing.enabled
[2904:3280:0219/073311:WARNING:pref_notifier_impl.cc(27)] pref observer found at shutdown plugins.allow_outdated
[2904:3280:0219/073311:WARNING:pref_notifier_impl.cc(27)] pref observer found at shutdown plugins.always_authorize
Backtrace:
	(No symbol) [0x61666544]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x02DCFC78+33833672]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x029F5C04+29794900]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x02DCFB91+33833441]
	ovly_debug_event [0x00CA5D1A+6638122]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x034FBB93+41353699]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x034FBC4B+41353883]
	ovly_debug_event [0x00CEFA46+6940502]
	ovly_debug_event [0x00CF020A+6942490]
	ovly_debug_event [0x00CF031B+6942763]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x036A59F8+43098184]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x0182F2F3+11155779]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x019E8F4E+12965278]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x019E4BA4+12947956]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x019E4BE1+12948017]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x019E6482+12954322]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x00E4800A+771674]
	ovly_debug_event [0x0086BD9B+2206379]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x01759607+10280023]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x017A2153+10577827]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x03DBD414+50535012]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x03C7FF7E+49235406]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x03C7FE36+49235078]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x03C7F3D3+49232419]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x03145348+37460376]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x00E075EB+506939]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x01085C44+3121812]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x01085DB9+3122185]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x01086389+3123673]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x010860D6+3122982]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x00E8BFCD+1050141]
	ovly_debug_event [0x00A75018+4341032]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x0313E1D8+37431336]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x00E343D6+690726]
	ovly_debug_event [0x00A75080+4341136]
	RelaunchChromeBrowserWithNewCommandLineIfNeeded [0x033E849A+40225514]
	RegisterWaitForInputIdle [0x7C816037+73]






Original issue's description:
> Handle RenderProcessHostImpl::SetBackgrounded on Windows
>
> This was disabled on Windows because:
>
>  - http://crrev.com/274071 made it such that it was asynchronous via the renderer (as only
> the process itself can set itself in background mode on Windows).
>
>  - And then this was removed for Windows as part of issue 381820 as true background mode on
> Windows was achieved by having the renderer itself change its process priority (which
> doesn't work as the unbackgrounding request can be stuck behind other priority tasks
> running in background mode).
>
> Also, the test for this was disabled in between (see issue 394368) -- the asynchronicity
> introduced in r274071 probably causing the flakes.
>
> Overall there is no need to have the renderer enter PROCESS_MODE_BACKGROUND_BEGIN itself,
> IDLE_PRIORITY_CLASS should be sufficient as its the same as far as CPU priority is
> concerned and IO is irrelevant in the renderers.
>
> Thus we can get background mode for hidden renderers without running into issue 381820.
>
> Experiment with IDLE_PRIORITY_CLASS/BELOW_NORMAL_PRIORITY_CLASS vs the status quo.
>
> Watching the relevant perf bots (tab_switching.top_10 -> MPArch.RWH_TabSwitchPaintDuration)
> and UMA metrics MPArch.RWH_TabSwitchPaintDuration which shouldn't regress.
> And others (e.g., SessionRestore related) which will hopefully improve.
>
> Enable the experiment by default in the absence of Finch to get perf waterfall coverage.
>
> The experiment will be called "BackgroundRendererProcesses" and have 4 groups:
>  ["Disallow", "AllowBelowNormalFromBrowser",
>   "AllowIdleFromBrowser", "AllowBackgroundModeFromRenderer"]
>
> It will be a per-session (rather than per-profile) experiment, randomly assigning a user
> to a group every new Chrome session.
>
> BUG=394368, 458594
>
> Committed: https://crrev.com/aaf738a2cce69ce952386b48e3bc252bd307ef43
> Cr-Commit-Position: refs/heads/master@{#317042}

TBR=wfh@chromium.org,jam@chromium.org,gab@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=394368, 458594
Committed: https://crrev.com/126d77b69d28f4e84117ae655f7414222982c881
Cr-Commit-Position: refs/heads/master@{#317070}

[Devlin, 2015-02-19 17:38:37]

Created Revert of Handle RenderProcessHostImpl::SetBackgrounded on Windows

[commit-bot: I haz the power, 2015-02-19 17:39:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/940993002/1

[commit-bot: I haz the power, 2015-02-19 17:39:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-19 17:40:51]

Patchset 1 (id:??) landed as
https://crrev.com/126d77b69d28f4e84117ae655f7414222982c881
Cr-Commit-Position: refs/heads/master@{#317070}