Revert of Split Screen mode implementation

Revert of Split Screen mode implementation (https://codereview.chromium.org/420603011/)

Reason for revert:
Appears to have broken Linux Chromium OS ASan LSan Tests (3) (stats):
http://build.chromium.org/p/chromium.memory/builders/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%283%29

athena_unittests failed 13
Basic
Accelerators
AppSelection
BasicTransition
VirtualKeyboardTransition
Basic
CreateContainer
GrabAndMouseCapture
GrabInputContainer
GrabShouldNotBlockVirtualKeyboard
NonActivatableContainer
Zorder
Empty

[ RUN      ] ActivityManagerTest.Basic
=================================================================
==8808==ERROR: AddressSanitizer: heap-use-after-free on address 0x60200000ad70 at pc 0x00000054eebe bp 0x7fff975aaa70 sp 0x7fff975aaa68
READ of size 8 at 0x60200000ad70 thread T0
#0 0x54eebd in __find<__gnu_cxx::__normal_iterator<athena::WindowManagerObserver **, std::vector<athena::WindowManagerObserver *, std::allocator<athena::WindowManagerObserver *> > >, athena::WindowManagerObserver *> /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/stl_algo.h:190:8
#1 0x54eebd in find<__gnu_cxx::__normal_iterator<athena::WindowManagerObserver **, std::vector<athena::WindowManagerObserver *, std::allocator<athena::WindowManagerObserver *> > >, athena::WindowManagerObserver *> /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/stl_algo.h:4402
#2 0x54eebd in ObserverListBase<athena::WindowManagerObserver>::RemoveObserver(athena::WindowManagerObserver*) base/observer_list.h:168
#3 0x560f79 in ~SplitViewController athena/wm/split_view_controller.cc:63:3
#4 0x560f79 in athena::SplitViewController::~SplitViewController() athena/wm/split_view_controller.cc:62
#5 0x54d340 in operator() base/memory/scoped_ptr.h:137:5
#6 0x54d340 in ~scoped_ptr_impl base/memory/scoped_ptr.h:220
#7 0x54d340 in ~scoped_ptr base/memory/scoped_ptr.h:432
#8 0x54d340 in athena::(anonymous namespace)::WindowManagerImpl::~WindowManagerImpl() athena/wm/window_manager_impl.cc:124
#9 0x54d57d in athena::(anonymous namespace)::WindowManagerImpl::~WindowManagerImpl() athena/wm/window_manager_impl.cc:116:41
#10 0x567127 in athena::ShutdownAthena() athena/main/athena_launcher.cc:86:3
#11 0x5657af in athena::test::AthenaTestHelper::TearDown() athena/test/athena_test_helper.cc:98:3
#12 0x5645b6 in athena::test::AthenaTestBase::TearDown() athena/test/athena_test_base.cc:51:3
#13 0x4fc938 in testing::TestInfo::Run() testing/gtest/src/gtest.cc:2610:5
#14 0x4fd676 in testing::TestCase::Run() testing/gtest/src/gtest.cc:2728:5
#15 0x5138f5 in testing::internal::UnitTestImpl::RunAllTests() testing/gtest/src/gtest.cc:4591:11
#16 0x512ee6 in HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> testing/gtest/src/gtest.cc:2418:12
#17 0x512ee6 in testing::UnitTest::Run() testing/gtest/src/gtest.cc:4209
#18 0x1602b74 in RUN_ALL_TESTS testing/gtest/include/gtest/gtest.h:2304:10
#19 0x1602b74 in base::TestSuite::Run() base/test/test_suite.cc:227
#20 0x15fa231 in Run base/callback.h:401:12
#21 0x15fa231 in base::(anonymous namespace)::LaunchUnitTestsInternal(base::Callback<int ()> const&, int, bool, base::Callback<void ()> const&) base/test/launcher/unit_test_launcher.cc:498
#22 0x15faf7e in base::LaunchUnitTestsSerially(int, char**, base::Callback<int ()> const&) base/test/launcher/unit_test_launcher.cc:564:10
#23 0x4d74ca in main athena/test/athena_unittests.cc:51:10
#24 0x7f9020d2d76c in __libc_start_main /build/buildd/eglibc-2.15/csu/libc-start.c:226
#25 0x4d726c in _start (/mnt/data/b/build/slave/Linux_Chromium_OS_ASan_LSan_Tests__3_/build/src/out/Release/athena_unittests+0x4d726c)

Please follow instructions on how to setup ASan on your workstation here: http://www.chromium.org/developers/testing/addresssanitizer
LSan may also be of use: http://www.chromium.org/developers/testing/leaksanitizer
You may also want run your patch through the linux_lsan try bot.

Original issue's description:
> Split Screen mode implementation.
> 
> Implements Split Screen mode and window cycling behavior.
> 
> BUG=383421
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288593

TBR=oshima,sadrul,mfomitchev,mukai
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288607

[please use gerrit instead, 2014-08-10 01:12:42]

Created Revert of Split Screen mode implementation

[commit-bot: I haz the power, 2014-08-10 01:13:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rouslan@chromium.org/451363002/1

[commit-bot: I haz the power, 2014-08-10 01:13:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-10 01:13:25]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[please use gerrit instead, 2014-08-10 01:18:50]

The CQ bit was checked by rouslan@chromium.org

[commit-bot: I haz the power, 2014-08-10 01:19:27]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rouslan@chromium.org/451363002/1

[commit-bot: I haz the power, 2014-08-10 01:24:24]

Change committed as 288607