Two HandleVerifier thread safety fixes.

base/win/scoped_handle.cc

Index: base/win/scoped_handle.cc
diff --git a/base/win/scoped_handle.cc b/base/win/scoped_handle.cc
index c429375b9cbb4a9a373508eb574b5e68627cc605..65b5b74762397418ee7fcfefb542846b27638a66 100644
--- a/base/win/scoped_handle.cc
+++ b/base/win/scoped_handle.cc
@@ -117,6 +117,8 @@ ActiveVerifier* ActiveVerifier::Get() {
 void ActiveVerifier::InstallVerifier() {
 #if defined(COMPONENT_BUILD)
   AutoNativeLock lock(g_lock.Get());
+  if (g_active_verifier)
+    return;
   g_active_verifier = new ActiveVerifier(true);
 #else
   // If you are reading this, wondering why your process seems deadlocked, take
@@ -128,17 +130,34 @@ void ActiveVerifier::InstallVerifier() {
       reinterpret_cast<GetHandleVerifierFn>(::GetProcAddress(
           main_module, "GetHandleVerifier"));
 
+  // This should only happen if running in a DLL is linked with base but the
+  // hosting EXE is not. In this case, create an ActiveVerifier for the current
+  // module but leave it disabled.
   if (!get_handle_verifier) {
     g_active_verifier = new ActiveVerifier(false);
     return;
   }
 
-  ActiveVerifier* verifier =
+  // Check if in the main module.
+  if (get_handle_verifier == GetHandleVerifier) {
+    AutoNativeLock lock(g_lock.Get());
+    if (g_active_verifier)
+      return;
+    g_active_verifier = new ActiveVerifier(true);
+    return;
+  }
+
+  ActiveVerifier* main_module_verifier =
       reinterpret_cast<ActiveVerifier*>(get_handle_verifier());
 
+  // Main module should always on-demand create a verifier.
+  DCHECK(main_module_verifier);
+
   // This lock only protects against races in this module, which is fine.
   AutoNativeLock lock(g_lock.Get());
-  g_active_verifier = verifier ? verifier : new ActiveVerifier(true);
+  if (g_active_verifier)

[scottmg, 2016/03/10 20:31:26]

Maybe an extra comment here describing what we discussed about this part.

[Will Harris, 2016/03/10 21:08:45]

Done.

+    return;
+  g_active_verifier = main_module_verifier;
 #endif
 }
 
@@ -221,7 +240,7 @@ void ActiveVerifier::OnHandleBeingClosed(HANDLE handle) {
 }  // namespace
 
 void* GetHandleVerifier() {
-  return g_active_verifier;
+  return ActiveVerifier::Get();
 }
 
 namespace base {