Move AlterEnvironment to base/environment.h, implement on Windows.

tools/gn/secondary/base/BUILD.gn

 # found in the LICENSE file.
 
 component("base") {
   sources = [
     "../build/build_config.h",
     "third_party/dmg_fp/dmg_fp.h",
     "third_party/dmg_fp/g_fmt.cc",
     "third_party/dmg_fp/dtoa_wrapper.cc",
     "third_party/icu/icu_utf.cc",
     "third_party/icu/icu_utf.h",
@@ skipping 382 matching lines @@
     "power_monitor/power_monitor_source.cc",
     "power_monitor/power_monitor_source.h",
     "power_monitor/power_observer.h",
     "process/internal_linux.cc",
     "process/internal_linux.h",
     "process/kill.cc",
     "process/kill.h",
     "process/kill_mac.cc",
     "process/kill_posix.cc",
     "process/kill_win.cc",
+    "process/launch.cc",
     "process/launch.h",
     "process/launch_ios.cc",
     "process/launch_mac.cc",
     "process/launch_posix.cc",
     "process/launch_win.cc",
     "process/memory.h",
     "process/memory_linux.cc",
     "process/memory_mac.mm",
     "process/memory_win.cc",
     "process/process.h",
@@ skipping 545 matching lines @@
 }
 
 static_library("run_all_unittests") {
   sources = [
     "test/run_all_unittests.cc",
   ]
   deps = [
     ":test_support_base",
   ]
 }