Move i420 files to the right location

There's also a presubmit check that disallows .. references
in GYP files, which this solves.

BUG=webrtc:5095
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1418753002 .

Cr-Commit-Position: refs/heads/master@{#10371}

webrtc/modules/modules.gyp

@@ -21,7 +21,7 @@
     'rtp_rtcp/rtp_rtcp.gypi',
     'utility/utility.gypi',
     'video_coding/codecs/h264/h264.gypi',
-    'video_coding/codecs/i420/main/source/i420.gypi',
+    'video_coding/codecs/i420/i420.gypi',
     'video_coding/video_coding.gypi',
     'video_capture/video_capture.gypi',
     'video_processing/video_processing.gypi',

webrtc/modules/video_coding/BUILD.gn

@@ -143,8 +143,8 @@ source_set("webrtc_h264") {
 
 source_set("webrtc_i420") {
   sources = [
-    "codecs/i420/main/interface/i420.h",
+    "codecs/i420/i420.cc",
-    "codecs/i420/main/source/i420.cc",
+    "codecs/i420/include/i420.h",
   ]
 
   configs += [ "../..:common_config" ]

webrtc/modules/video_coding/codecs/i420/i420.cc

@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "webrtc/modules/video_coding/codecs/i420/main/interface/i420.h"
+#include "webrtc/modules/video_coding/codecs/i420/include/i420.h"
 
 #include <limits>
 #include <string>

webrtc/modules/video_coding/codecs/i420/i420.gypi

@@ -15,7 +15,7 @@
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
       ],
       'sources': [
-        '../interface/i420.h',
+        'include/i420.h',
         'i420.cc',
       ],
     },

webrtc/modules/video_coding/main/source/codec_database.cc

@@ -18,7 +18,7 @@
 #include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
 #endif
 #ifdef VIDEOCODEC_I420
-#include "webrtc/modules/video_coding/codecs/i420/main/interface/i420.h"
+#include "webrtc/modules/video_coding/codecs/i420/include/i420.h"
 #endif
 #ifdef VIDEOCODEC_VP8
 #include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"