Revert of base: Enable browser-wide discardable memory on Linux, CrOS and Windows.

Revert of base: Enable browser-wide discardable memory on Linux, CrOS and Windows. (patchset #1 id:1 of https://codereview.chromium.org/793443003/)

Reason for revert:
Likely causing many crashes in layout tests on chromium.webkit's WebKit Win7 (dbg) builder as well as tryserver's win_blink_rel.

The failures started here:
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Win7%20%28dbg%29/builds/9070

Excerpt from log:
15:14:22.485 352 worker/3 virtual/deferred/inspector/tracing/timeline-style-recalc-with-invalidations.html crashed, (stderr lines):
15:14:22.485 352   [4300:4244:0106/151422:991308:FATAL:host_discardable_shared_memory_manager.cc(126)] Check failed: bytes_allocated_ >= size (0 vs. 4194304)
15:14:22.485 352   Backtrace:
15:14:22.485 352   	base::debug::StackTrace::StackTrace [0x008CA731+33]
15:14:22.485 352   	logging::LogMessage::~LogMessage [0x0095B6FF+63]
15:14:22.485 352   	content::HostDiscardableSharedMemoryManager::ProcessRemoved [0x117B47DB+283]
15:14:22.485 352   	content::RenderMessageFilter::~RenderMessageFilter [0x10DD88B4+628]
15:14:22.485 352   	content::RenderMessageFilter::`vector deleting destructor' [0x10DD9DC7+87]
15:14:22.485 352   	content::BrowserThread::DeleteOnThread<6>::Destruct<content::RenderMessageFilter> [0x10DC7A95+85]
15:14:22.485 352   	content::RenderMessageFilter::OnDestruct [0x10DDD437+23]
15:14:22.485 352   	content::BrowserMessageFilterTraits::Destruct [0x102F99B3+19]
15:14:22.485 352   	base::RefCountedThreadSafe<content::BrowserMessageFilter,content::BrowserMessageFilterTraits>::Release [0x102FA602+82]
15:14:22.485 352   	scoped_refptr<content::BrowserMessageFilter>::Release [0x102FA63E+14]
15:14:22.485 352   	scoped_refptr<content::BrowserMessageFilter>::~scoped_refptr<content::BrowserMessageFilter> [0x102F8D91+33]
15:14:22.485 352   	content::BrowserMessageFilter::Internal::~Internal [0x102F8FA3+35]
15:14:22.485 352   	content::BrowserMessageFilter::Internal::`scalar deleting destructor' [0x102F9536+22]
15:14:22.485 352   	base::RefCountedThreadSafe<IPC::MessageFilter,base::DefaultRefCountedThreadSafeTraits<IPC::MessageFilter> >::DeleteInternal [0x05C16FDF+63]
15:14:22.485 352   	base::DefaultRefCountedThreadSafeTraits<IPC::MessageFilter>::Destruct [0x05C1704C+12]
15:14:22.485 352   	base::RefCountedThreadSafe<IPC::MessageFilter,base::DefaultRefCountedThreadSafeTraits<IPC::MessageFilter> >::Release [0x05C18D92+82]
15:14:22.485 352   	scoped_refptr<IPC::MessageFilter>::Release [0x05C18DEE+14]
15:14:22.485 352   	scoped_refptr<IPC::MessageFilter>::~scoped_refptr<IPC::MessageFilter> [0x05C13CD1+33]
15:14:22.485 352   	scoped_refptr<IPC::MessageFilter>::`scalar deleting destructor' [0x05C15E36+22]
15:14:22.485 352   	std::allocator<scoped_refptr<IPC::MessageFilter> >::destroy<scoped_refptr<IPC::MessageFilter> > [0x05C11698+24]
15:14:22.485 352   	std::allocator_traits<std::allocator<scoped_refptr<IPC::MessageFilter> > >::destroy<scoped_refptr<IPC::MessageFilter> > [0x05C116CF+15]
15:14:22.485 352   	std::_Wrap_alloc<std::allocator<scoped_refptr<IPC::MessageFilter> > >::destroy<scoped_refptr<IPC::MessageFilter> > [0x05C1165B+27]
15:14:22.485 352   	std::_Destroy_range<std::_Wrap_alloc<std::allocator<scoped_refptr<IPC::MessageFilter> > > > [0x05C103C2+34]
15:14:22.485 352   	std::_Destroy_range<std::_Wrap_alloc<std::allocator<scoped_refptr<IPC::MessageFilter> > > > [0x05C10374+52]
15:14:22.485 352   	std::vector<scoped_refptr<IPC::MessageFilter>,std::allocator<scoped_refptr<IPC::MessageFilter> > >::_Destroy [0x05C1A867+55]
15:14:22.485 352   	std::vector<scoped_refptr<IPC::MessageFilter>,std::allocator<scoped_refptr<IPC::MessageFilter> > >::clear [0x05C1B647+55]
15:14:22.485 352   	IPC::ChannelProxy::Context::OnChannelClosed [0x05C17A0F+207]

Original issue's description:
> base: Enable browser-wide discardable memory on Linux, CrOS and Windows.
>
> This makes SHMEM implementation of discardable memory preferred
> over EMULATED implementation. This effectively makes SHMEM the
> implementation used by default on Linux, CrOS and Windows.
>
> SHMEM implementation of discardable memory gives the browser
> process control over the total amount of discardable memory used
> and allows us to enforce a global limit of 512MB across all
> renderers.
>
> BUG=429415, 429416
>
> Committed: https://crrev.com/03ea50508953461c007316ef0bf2d5c68d097d4b
> Cr-Commit-Position: refs/heads/master@{#310153}

TBR=avi@chromium.org,danakj@chromium.org,reveman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=429415, 429416
Committed: https://crrev.com/c6ae3d0b139fef665294fee543b4016777880672
Cr-Commit-Position: refs/heads/master@{#310227}

[falken, 2015-01-07 03:22:54]

Created Revert of base: Enable browser-wide discardable memory on Linux, CrOS
and Windows.

[commit-bot: I haz the power, 2015-01-07 03:23:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/812993007/1

[commit-bot: I haz the power, 2015-01-07 03:24:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-07 03:25:31]

Patchset 1 (id:??) landed as
https://crrev.com/c6ae3d0b139fef665294fee543b4016777880672
Cr-Commit-Position: refs/heads/master@{#310227}