Introduce WebRTC component build.

This CL switches all the Chromium dependencies from being direct
dependencies on WebRTC targets to a WebRTC component (which lives
at //third_party/webrtc_overrides:webrtc_component).

From now on, Chromium should never directly depend on WebRTC in
order to avoid issues explained at [1] (this will be guarded
by checkdeps and GN visibility (see [2])) but should only depend
on the WebRTC component.

This should solve a broad range of problems caused by WebRTC being
linked in different shared libraries when is_component_build=true
(from globals and singletons causing hard to debug issues, to ODR
violations and binary size increase).

[1] - https://chromium.googlesource.com/chromium/src.git/+/master/docs/component_build.md#dependencies-between-targets
[2] - https://webrtc-review.googlesource.com/c/src/+/154344

TBR: [email protected]
Bug: webrtc:9419
Change-Id: Ice56827db1753f51592165a90c1094b468c8e188
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1874722
Commit-Queue: Mirko Bonadei <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Reviewed-by: Tommi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#715450}
diff --git a/DEPS b/DEPS
index cce16a6..44f74ee 100644
--- a/DEPS
+++ b/DEPS
@@ -1502,7 +1502,7 @@
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + 'dd55f3ca8f2ea716ca917a4aaf36f0729fe902b1',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + 'eb48799ec5048459b2b5e00b6d940ddcf76c72d9',
+    Var('webrtc_git') + '/src.git' + '@' + '02fac7d86e64595d6c35c1460e491d7f04c01864',
 
   # Wuffs' canonical repository is at github.com/google/wuffs, but we use
   # Skia's mirror of Wuffs, the same as in upstream Skia's DEPS file.