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/scroll_bounce_flag.patch

@@ -0,0 +1,13 @@
+diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
+index 81d3f80..a8c4a57 100644
+--- a/content/renderer/render_thread_impl.cc
++++ b/content/renderer/render_thread_impl.cc
+@@ -1737,7 +1737,7 @@ bool RenderThreadImpl::IsGpuMemoryBufferCompositorResourcesEnabled() {
+ }
+ 
+ bool RenderThreadImpl::IsElasticOverscrollEnabled() {
+-  return is_elastic_overscroll_enabled_;
++  return base::CommandLine::ForCurrentProcess()->HasSwitch("scroll-bounce");
+ }
+ 
+ scoped_refptr<base::SingleThreadTaskRunner>