Set msvs_error_on_missing_sources=1 in GYP_GENERATOR_FLAGS on Windows.

This will make us detect when sources are listed in GYP files that
are no longer present on disk. This check only exists for Windows
but should be enough to keep our GYP files up to date with the file
system.

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/54409004

Cr-Commit-Position: refs/heads/master@{#9187}

webrtc/build/gyp_webrtc

@@ -70,6 +70,13 @@ if __name__ == '__main__':
   if not os.environ.get('GYP_GENERATORS'):
     os.environ['GYP_GENERATORS'] = 'ninja'
 
+  # Enable check for missing sources in GYP files on Windows.
+  if sys.platform.startswith('win'):
+    gyp_generator_flags = os.getenv('GYP_GENERATOR_FLAGS', '')
+    if not 'msvs_error_on_missing_sources' in gyp_generator_flags:
+      os.environ['GYP_GENERATOR_FLAGS'] = (
+          gyp_generator_flags + ' msvs_error_on_missing_sources=1')
+
   vs2013_runtime_dll_dirs = None
   if int(os.environ.get('DEPOT_TOOLS_WIN_TOOLCHAIN', '1')):
     vs2013_runtime_dll_dirs = vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()

webrtc/video_engine/BUILD.gn

@@ -14,15 +14,6 @@ source_set("video_engine") {
 
 source_set("video_engine_core") {
   sources = [
-    "include/vie_base.h",
-    "include/vie_capture.h",
-    "include/vie_codec.h",
-    "include/vie_errors.h",
-    "include/vie_external_codec.h",
-    "include/vie_image_process.h",
-    "include/vie_network.h",
-    "include/vie_render.h",
-    "include/vie_rtp_rtcp.h",
     "call_stats.cc",
     "call_stats.h",
     "encoder_state_feedback.cc",

webrtc/video_engine/video_engine_core.gypi

@@ -35,17 +35,6 @@
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
       ],
       'sources': [
-        # interface
-        'include/vie_base.h',
-        'include/vie_capture.h',
-        'include/vie_codec.h',
-        'include/vie_errors.h',
-        'include/vie_external_codec.h',
-        'include/vie_image_process.h',
-        'include/vie_network.h',
-        'include/vie_render.h',
-        'include/vie_rtp_rtcp.h',
-
         # headers
         'call_stats.h',
         'encoder_state_feedback.h',