Fix linker errors about v8::AssertNoGCScope on Windows
Fix linker errors about v8::AssertNoGCScope on Windows

    [8/9] LINK(DLL) chromiumcontent.dll
    FAILED: D:\Python27\python.exe gyp-win-tool link-wrapper environment.x86 link.exe /nologo /IMPLIB:chromiumcontent.dll.lib /DLL /OUT:chromiumcontent.dll /PDB:chromiumcontent.dll.pdb @chromiumcontent.dll.rsp && D:\Python27\python.exe gyp-win-tool manifest-wrapper environment.x86 cmd /c if exist chromiumcontent.dll.manifest del chromiumcontent.dll.manifest && D:\Python27\python.exe gyp-win-tool manifest-wrapper environment.x86 mt.exe -nologo -manifest obj\chromiumcontent\chromiumcontent.chromiumcontent.dll.intermediate.manifest -out:chromiumcontent.dll.manifest
    v8_base.ia32.lib(v8_base.ia32.api.obj) : error LNK2005: "private: __thiscall v8::AssertNoGCScope::AssertNoGCScope(class v8::Isolate *)" (??0AssertNoGCScope@v8@@AAE@PAVIsolate@1@@Z) already defined in webcore_rendering.lib(webcore_rendering.stylevisualdata.obj)

V8 is using the DEBUG macro to control how v8::AssertNoGCScope is compiled. But
not all projects define a DEBUG macro in their Debug configurations. So now we
switch V8 to use NDEBUG instead, which is used everywhere.

paulcbetts/libchromiumcontent,adamjgray/libchromiumcontent,synaptek/libchromiumcontent,eric-seekas/libchromiumcontent,zhanggyb/libchromiumcontent,hokein/libchromiumcontent,atom/libchromiumcontent,adamjgray/libchromiumcontent,bbondy/libchromiumcontent,electron/libchromiumcontent,electron/libchromiumcontent,deepak1556/libchromiumcontent,eric-seekas/libchromiumcontent,hokein/libchromiumcontent,atom/libchromiumcontent,deepak1556/libchromiumcontent,zhanggyb/libchromiumcontent,paulcbetts/libchromiumcontent,jlord/libchromiumcontent,jlord/libchromiumcontent,bbondy/libchromiumcontent,brave/libchromiumcontent,synaptek/libchromiumcontent,brave/libchromiumcontent