Merge pull request #3048 from maxwell-demon/timespec

BUILD

build.json

gRPC.podspec

include/grpc/support/time.h

src/core/profiling/basic_timers.c

src/core/support/time_posix.c

src/core/support/time_precise.h

src/core/support/time_win32.c

tools/doxygen/Doxyfile.core.internal

tools/run_tests/sources_and_headers.json

vsprojects/gpr/gpr.vcxproj

vsprojects/gpr/gpr.vcxproj.filters

vsprojects/grpc/grpc.vcxproj

vsprojects/grpc/grpc.vcxproj.filters

vsprojects/grpc_unsecure/grpc_unsecure.vcxproj

vsprojects/grpc_unsecure/grpc_unsecure.vcxproj.filters