Add new dependency on targets that use i420_buffer.h

WebRTC api:video_frame_api is splitting into two targets, and all
targets that include i420_buffer.h must depend on a new target
api:video_frame_api_i420. This CL fixes that for Chromium.

Bug: webrtc:7504
Change-Id: Ic383a5592a5b01a4463565326fe4fecd2fc96829
Reviewed-on: https://chromium-review.googlesource.com/776715Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Commit-Queue: Patrik Höglund <phoglund@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517848}

content/renderer/BUILD.gn

@@ -915,6 +915,7 @@ target(link_target_type, "renderer") {
       "//third_party/webrtc/api:optional",
       "//third_party/webrtc/api:rtc_stats_api",
       "//third_party/webrtc/api:video_frame_api",
+      "//third_party/webrtc/api:video_frame_api_i420",
       "//third_party/webrtc/api/audio_codecs:audio_codecs_api",
       "//third_party/webrtc/api/audio_codecs/L16:audio_decoder_L16",
       "//third_party/webrtc/api/audio_codecs/L16:audio_encoder_L16",

content/test/BUILD.gn

@@ -1829,6 +1829,7 @@ test("content_unittests") {
       "//third_party/webrtc/api:libjingle_peerconnection",
       "//third_party/webrtc/api:rtc_stats_api",
       "//third_party/webrtc/api:video_frame_api",
+      "//third_party/webrtc/api:video_frame_api_i420",
       "//third_party/webrtc/api/video_codecs:video_codecs_api",
       "//third_party/webrtc/media:rtc_media",
       "//third_party/webrtc/modules/desktop_capture:primitives",