Revert "Move files in wtf/ to platform/wtf/"

This reverts 2 CLs:
https://codereview.chromium.org/2771783003
https://codereview.chromium.org/2767153004

Compilation on Windows was broken after r459386 if is_component_build=true.
[6/3401] LINK(DLL) blink_platform.dll blink_platform.dll.lib blink_platform.dll.pdb
FAILED: blink_platform.dll blink_platform.dll.lib blink_platform.dll.pdb
C:/python_27_amd64/files/python.exe ../../build/toolchain/win/tool_wrapper.py link-wrapper environment.x64 False link.exe /nologo /IMPLIB:./blink_platform.dll.lib /DLL /OUT:./blink_platform.dll /PDB:./blink_platform.dll.pdb @./blink_platform.dll.rsp
LINK : fatal error LNK1104: cannot open file 'wtf.dll.lib'
[55/3401] CXX irt_x64/obj/third_party/icu/icui18n/tzfmt.o
ninja: build stopped: subcommand failed.

'wtf.dll.lib' isn't created because it doesn't contain any symbols to export.

BUG=691465
TBR=yutak@chromium.org

Review-Url: https://codereview.chromium.org/2774333002
Cr-Commit-Position: refs/heads/master@{#459796}
76 files changed