Here is the build log.

lwchkg@I7-4790 F:\chromium\src
> ..\build_unittests
ninja: Entering directory `F:\chromium\src\out\gn_debug'
[21/1961] CXX obj/third_party/WebKit/Source/platform/platform/platform_jumbo_3.obj
FAILED: obj/third_party/WebKit/Source/platform/platform/platform_jumbo_3.obj
ninja -t msvc -e environment.x86 -- "c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.11.25503\bin\hostx64\x86/cl.exe" /nologo /showIncludes  @obj/third_party/WebKit/Source/platform/platform/platform_jumbo_3.obj.rsp /c gen/third_party/WebKit/Source/platform/platform_jumbo_3.cc /Foobj/third_party/WebKit/Source/platform/platform/platform_jumbo_3.obj /Fd"obj/third_party/WebKit/Source/platform/platform_cc.pdb"
f:\chromium\src\out\gn_debug\gen\third_party\webkit\source\platform\../../../../../../../third_party/WebKit/Source/platform/fonts/FontVariantNumeric.cpp(11): error C2374: 'blink::kUnknownString': redefinition; multiple initialization
f:\chromium\src\out\gn_debug\gen\third_party\webkit\source\platform\../../../../../../../third_party/WebKit/Source/platform/fonts/FontVariantEastAsian.cpp(11): note: see declaration of 'blink::kUnknownString'
[30/1961] CXX obj/third_party/pdfium/javascript/Document.obj
ninja: build stopped: subcommand failed.