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/chromium/allow_nested_error_trackers.patch

@@ -0,0 +1,13 @@
+diff --git a/ui/gfx/x/x11_error_tracker.cc b/ui/gfx/x/x11_error_tracker.cc
+index af031de356c5..2a5c18dc473a 100644
+--- a/ui/gfx/x/x11_error_tracker.cc
++++ b/ui/gfx/x/x11_error_tracker.cc
+@@ -24,7 +24,7 @@ namespace gfx {
+ X11ErrorTracker::X11ErrorTracker() {
+   // This is a non-exhaustive check for incorrect usage. It disallows nested
+   // X11ErrorTracker instances on the same thread.
+-  DCHECK(g_handler == NULL);
++  // DCHECK(g_handler == NULL);
+   g_handler = this;
+   XSync(GetXDisplay(), False);
+   old_handler_ = XSetErrorHandler(X11ErrorHandler);