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/out_of_process_instance.patch

@@ -0,0 +1,15 @@
+diff --git a/pdf/out_of_process_instance.cc b/pdf/out_of_process_instance.cc
+index 8b9c9f19a3dd..c4d801135053 100644
+--- a/pdf/out_of_process_instance.cc
++++ b/pdf/out_of_process_instance.cc
+@@ -333,7 +333,9 @@ bool OutOfProcessInstance::Init(uint32_t argc,
+   std::string document_url = document_url_var.AsString();
+   base::StringPiece document_url_piece(document_url);
+   is_print_preview_ = IsPrintPreviewUrl(document_url_piece);
+-  if (!document_url_piece.starts_with(kChromeExtension) && !is_print_preview_)
++  if (!document_url_piece.starts_with(kChromeExtension) &&
++      !document_url_piece.starts_with("chrome://pdf-viewer") &&
++      !is_print_preview_)
+     return false;
+ 
+   // Check if the plugin is full frame. This is passed in from JS.