From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andy Locascio <andy@slack-corp.com>
Date: Tue, 18 Feb 2020 14:35:04 -0800
Subject: content: allow embedder to prevent locking scheme registry

The //content layer requires all schemes to be registered during startup,
because Add*Scheme aren't threadsafe. However, Electron exposes the option to
register additional schemes via JavaScript in the main process before the app
is ready, but after the //content layer has already locked the registry.

This allows embedders to optionally keep the scheme registry unlocked, and it
is their responsibility to ensure that it is not accessed in a way that would
cause potential thread-safety issues.

Previously upstreamed patch: https://chromium-review.googlesource.com/c/chromium/src/+/1637040

This change was lost during upstream refactor in
https://chromium-review.googlesource.com/c/chromium/src/+/1901591, we should try
re-submitting the patch.

diff --git a/content/app/content_main_runner_impl.cc b/content/app/content_main_runner_impl.cc
index 095bc943529c38c4f469bf69b79006ca48a4e0d5..0e358e2d140bccf2e987db234cd5922732149168 100644
--- a/content/app/content_main_runner_impl.cc
+++ b/content/app/content_main_runner_impl.cc
@@ -751,7 +751,7 @@ int ContentMainRunnerImpl::Initialize(const ContentMainParams& params) {
   }
 #endif
 
-  RegisterContentSchemes();
+  RegisterContentSchemes(delegate_->ShouldLockSchemeRegistry());
   ContentClientInitializer::Set(process_type, delegate_);
 
 #if !defined(OS_ANDROID)
diff --git a/content/common/url_schemes.cc b/content/common/url_schemes.cc
index 29d38782f197cb72a875effab00ffc7960435ac1..694fe67ef751b2a84d8fc3f5ad82854fe2287a11 100644
--- a/content/common/url_schemes.cc
+++ b/content/common/url_schemes.cc
@@ -50,7 +50,7 @@ std::vector<std::string>& GetMutableServiceWorkerSchemes() {
 
 }  // namespace
 
-void RegisterContentSchemes() {
+void RegisterContentSchemes(bool should_lock_registry) {
   // On Android and in tests, schemes may have been registered already.
   if (g_registered_url_schemes)
     return;
@@ -110,7 +110,8 @@ void RegisterContentSchemes() {
   // threadsafe so must be called when GURL isn't used on any other thread. This
   // is really easy to mess up, so we say that all calls to Add*Scheme in Chrome
   // must be inside this function.
-  url::LockSchemeRegistries();
+  if (should_lock_registry)
+    url::LockSchemeRegistries();
 
   // Combine the default savable schemes with the additional ones given.
   GetMutableSavableSchemes().assign(std::begin(kDefaultSavableSchemes),
diff --git a/content/common/url_schemes.h b/content/common/url_schemes.h
index 3038f9d25798f36811b6398f8cc0e7d83ecc41b0..68189c36c47ef85b345b0ccc40c456f889977bee 100644
--- a/content/common/url_schemes.h
+++ b/content/common/url_schemes.h
@@ -16,7 +16,7 @@ namespace content {
 // parsed as "standard" or "referrer" with the src/url/ library, then locks the
 // sets of schemes down. The embedder can add additional schemes by
 // overriding the ContentClient::AddAdditionalSchemes method.
-CONTENT_EXPORT void RegisterContentSchemes();
+CONTENT_EXPORT void RegisterContentSchemes(bool should_lock_registry = true);
 
 // Re-initializes schemes for tests.
 CONTENT_EXPORT void ReRegisterContentSchemesForTests();
diff --git a/content/public/app/content_main_delegate.cc b/content/public/app/content_main_delegate.cc
index 8c71a579ee69d77547698c2135e3b4453c126b97..9b7fd8949b13d97982a100a36d9f73c9947b8853 100644
--- a/content/public/app/content_main_delegate.cc
+++ b/content/public/app/content_main_delegate.cc
@@ -42,6 +42,10 @@ bool ContentMainDelegate::ShouldHandleConsoleControlEvents() {
 }
 #endif
 
+bool ContentMainDelegate::ShouldLockSchemeRegistry() {
+  return true;
+}
+
 bool ContentMainDelegate::ShouldCreateFeatureList() {
   return true;
 }
diff --git a/content/public/app/content_main_delegate.h b/content/public/app/content_main_delegate.h
index 5e45724edf07ac33c9a423ecb6b6077f19e13b04..84f77390772828554e446d1e6f99198b76e9f835 100644
--- a/content/public/app/content_main_delegate.h
+++ b/content/public/app/content_main_delegate.h
@@ -69,6 +69,20 @@ class CONTENT_EXPORT ContentMainDelegate {
   // returning initialization error code. Default behavior is CHECK(false).
   virtual int TerminateForFatalInitializationError();
 
+  // Allows the embedder to prevent locking the scheme registry. The scheme
+  // registry is the list of URL schemes we recognize, with some additional
+  // information about each scheme such as whether it expects a host. The
+  // scheme registry is not thread-safe, so by default it is locked before any
+  // threads are created to ensure single-threaded access. An embedder can
+  // override this to prevent the scheme registry from being locked during
+  // startup, but if they do so then they are responsible for making sure that
+  // the registry is only accessed in a thread-safe way, and for calling
+  // url::LockSchemeRegistries() when initialization is complete. If possible,
+  // prefer registering additional schemes through
+  // ContentClient::AddAdditionalSchemes over preventing the scheme registry
+  // from being locked.
+  virtual bool ShouldLockSchemeRegistry();
+
   // Allows the embedder to perform platform-specific initialization before
   // BrowserMain() is invoked (i.e. before BrowserMainRunner, BrowserMainLoop,
   // BrowserMainParts, etc. are created).
