build: move libcc patches to electron repo (#14104)

In the GN build, libchromiumcontent is no longer a distinct library, but
merely a container for a set of scripts and patches. Maintaining those
patches in a separate repository is tedious and error-prone, so merge
them into the main repo.

Once this is merged and GN is the default way to build Electron, the
libchromiumcontent repository can be archived.

patches/common/webrtc/disable-warning-win.patch

@@ -0,0 +1,16 @@
+diff --git a/rtc_base/thread.cc b/rtc_base/thread.cc
+index 1bc0c0cd8..51208e4f0 100644
+--- a/rtc_base/thread.cc
++++ b/rtc_base/thread.cc
+@@ -23,7 +23,10 @@
+ #include "rtc_base/stringutils.h"
+ #include "rtc_base/timeutils.h"
+ #include "rtc_base/trace_event.h"
+-
++#ifdef _WIN32
++//Warning on windows because ThreadManager destructor never returns
++#pragma warning(disable:4722)
++#endif
+ namespace rtc {
+ 
+ ThreadManager* ThreadManager::Instance() {