libjpeg headers (jmorecfg.h):
typedef int boolean

Windows headers:
typedef unsigned char boolean

When the jpeg decoder and Windows headers are in the same translation units they will collide. 

libjpeg has a hook to predefine boolean, probably because of this, so that is probably the way to get out of this in jumbo builds.

Alternatively exclude the jpeg image decoder from jumbo.

Error message:

FAILED: obj/third_party/WebKit/Source/platform/platform/platform_jumbo_6.obj
ninja -t msvc -e environment.x64 -- "c:\program files (x86)\microsoft visual studio\2017\professional\vc\tools\msvc\14.11.25503\bin\hostx64\x64/cl.exe" /nologo /showIncludes @obj/third_party/WebKit/Source/platform/platform/platform_jumbo_6.obj.rsp /c gen/third_party/WebKit/Source/platform/platform_jumbo_6.cc /Foobj/third_party/WebKit/Source/platform/platform/platform_jumbo_6.obj /Fd"obj/third_party/WebKit/Source/platform/platform_cc.pdb"
c:\program files (x86)\windows kits\10\include\10.0.15063.0\shared\rpcndr.h(193): error C2371: 'boolean': redefinition; different basic types
l:\src\clean_chromium\src\third_party\libjpeg_turbo\jmorecfg.h(242): note: see declaration of 'boolean'
c:\program files (x86)\windows kits\10\include\10.0.15063.0\shared\wtypesbase.h(501): error C2371: 'BOOLEAN': redefinition; different basic types
c:\program files (x86)\windows kits\10\include\10.0.15063.0\um\winnt.h(1102): note: see declaration of 'BOOLEAN'
ninja: build stopped: subcommand failed.

In this particular case this was triggered by the combination of image-decoders/jpeg/JPEGImageDecoder.cpp and clipboard/ClipboardUtilitiesWin.cpp which are about 85 files apart in the file list so a smaller jumbo chunk size would hide this problem as well.