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 1f05e6351c58cbd9e65bd48ddd4e9a4eb8c7fbf1..c865e271a45fa35f4dadc0e845392607a209c2c8 100644
--- a/content/app/content_main_runner_impl.cc
+++ b/content/app/content_main_runner_impl.cc
@@ -702,7 +702,7 @@ 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 dc37f121130d83e200d73dd1ad566847548ac0fd..63080c1bc486a488841fc5d2081f4d5d4a00bde3 100644
--- a/content/common/url_schemes.cc
+++ b/content/common/url_schemes.cc
@@ -49,7 +49,7 @@ 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;
@@ -106,7 +106,8 @@ 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 e6379748886956da819523200aa35f8f95d523ee..46110a92ba9849112889f3e93c1dccbbd4911dda 100644
--- a/content/public/app/content_main_delegate.cc
+++ b/content/public/app/content_main_delegate.cc
@@ -36,6 +36,10 @@ int ContentMainDelegate::TerminateForFatalInitializationError() {
   return 0;
 }
 
+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 abb46995385fccddf8363296fb0253624a4111c7..715d0818c03cfa7e5b9877b3ab83d1488f2f040f 100644
--- a/content/public/app/content_main_delegate.h
+++ b/content/public/app/content_main_delegate.h
@@ -65,6 +65,20 @@ 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
   // creating the main message loop.
   virtual void PreCreateMainMessageLoop() {}
