Bug 1163103 - stop using NS_GetSpecialDirectory off the main thread within the cycle collector (via nsDumpUtils.cpp), r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D42856

--HG--
extra : moz-landing-system : lando

xpcom/base/moz.build

@@ -133,10 +133,14 @@ EXPORTS.mozilla += [
     'TupleCycleCollection.h',
 ]
 
+SOURCES += [
 # nsDebugImpl isn't unified because we disable PGO so that NS_ABORT_OOM isn't
 # optimized away oddly.
-SOURCES += [
     'nsDebugImpl.cpp',
+# nsDumpUtils.cpp includes SpecialSystemDirectory.h which includes
+# nsLocalFileMac.h which upsets other files in this dir that have a different
+# idea about what `TextRange` means.
+    'nsDumpUtils.cpp',
 ]
 SOURCES['nsDebugImpl.cpp'].no_pgo = True
 
@@ -164,7 +168,6 @@ UNIFIED_SOURCES += [
     'nsCycleCollectionParticipant.cpp',
     'nsCycleCollector.cpp',
     'nsCycleCollectorTraceJSHelpers.cpp',
-    'nsDumpUtils.cpp',
     'nsErrorService.cpp',
     'nsGZFileWriter.cpp',
     'nsID.cpp',

xpcom/base/nsDumpUtils.cpp

@@ -13,6 +13,7 @@
 #include "nsIObserverService.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/Unused.h"
+#include "SpecialSystemDirectory.h"
 
 #ifdef XP_UNIX  // {
 #  include "mozilla/Preferences.h"
@@ -417,7 +418,12 @@ nsresult nsDumpUtils::OpenTempFile(const nsACString& aFilename, nsIFile** aFile,
 #endif
   nsresult rv;
   if (!*aFile) {
-    rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, aFile);
+    if (NS_IsMainThread()) {
+      // This allows tests to override, but isn't safe off-mainthread.
+      rv = NS_GetSpecialDirectory(NS_OS_TEMP_DIR, aFile);
+    } else {
+      rv = GetSpecialSystemDirectory(OS_TemporaryDirectory, aFile);
+    }
     if (NS_WARN_IF(NS_FAILED(rv))) {
       return rv;
     }