Isolating APM API build target: add dependency on :api target.

This CL is part of a refactoring work to unblock other CLs
that would generate a circular dependency when including
modules/audio_processing in WebRTC. It will also allow to easily move
the APM interface part under //api (in WebRTC).

More in detail, this change adds :api as dependency in chromium
where needed. The target is currently a dummy one
(see https://webrtc-review.googlesource.com/c/src/+/109585), but
once this CL lands, https://webrtc-review.googlesource.com/c/src/+/109501
will make it an actual target.

Bug: webrtc:9535
Change-Id: Iffa36ff948369f172970edb53917fccdcb07e05b
Reviewed-on: https://chromium-review.googlesource.com/c/1319674Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Ale Bzk <alessiob@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605795}

content/renderer/BUILD.gn

@@ -732,6 +732,7 @@ target(link_target_type, "renderer") {
     "//third_party/webrtc/media:rtc_media_base",
     "//third_party/webrtc/modules/audio_device",
     "//third_party/webrtc/modules/audio_processing",
+    "//third_party/webrtc/modules/audio_processing:api",
     "//third_party/webrtc/modules/audio_processing:audio_processing_statistics",
     "//third_party/webrtc/modules/audio_processing/aec_dump",
     "//third_party/webrtc/modules/video_coding:video_codec_interface",

media/webrtc/BUILD.gn

@@ -29,6 +29,7 @@ component("webrtc") {
   deps = [
     "//base",
     "//third_party/webrtc/modules/audio_processing",
+    "//third_party/webrtc/modules/audio_processing:api",
     "//third_party/webrtc/modules/audio_processing:audio_processing_statistics",
     "//third_party/webrtc_overrides:init_webrtc",
   ]