Bug 1640087: Part 1: optimize read ahead DLL prefetches for nightly users r=dthayer

Differential Revision: https://phabricator.services.mozilla.com/D76519

toolkit/xre/nsAppRunner.cpp

@@ -3595,6 +3595,13 @@ static void ReadAheadPackagedDll(const wchar_t* dllName,
 static void PR_CALLBACK ReadAheadDlls_ThreadStart(void* arg) {
   UniquePtr<wchar_t[]> greDir(static_cast<wchar_t*>(arg));
 
+  // In Bug 1628903, we investigated which DLLs we should prefetch in
+  // order to reduce disk I/O and improve startup on Windows machines.
+  // Our ultimate goal is to measure the impact of these improvements on
+  // retention (see Bug 1640087). Before we place this within a pref,
+  // we should ensure this feature only ships to the nightly channel
+  // and monitor results from that subset.
+#  ifdef NIGHTLY_BUILD
   // Prefetch the DLLs shipped with firefox
   ReadAheadPackagedDll(L"libegl.dll", greDir.get());
   ReadAheadPackagedDll(L"libGLESv2.dll", greDir.get());
@@ -3605,6 +3612,21 @@ static void PR_CALLBACK ReadAheadDlls_ThreadStart(void* arg) {
   // Prefetch the system DLLs
   ReadAheadSystemDll(L"DWrite.dll");
   ReadAheadSystemDll(L"D3DCompiler_47.dll");
+#  else
+  // Load DataExchange.dll and twinapi.appcore.dll for
+  // nsWindow::EnableDragDrop
+  ReadAheadSystemDll(L"DataExchange.dll");
+  ReadAheadSystemDll(L"twinapi.appcore.dll");
+
+  // Load twinapi.dll for WindowsUIUtils::UpdateTabletModeState
+  ReadAheadSystemDll(L"twinapi.dll");
+
+  // Load explorerframe.dll for WinTaskbar::Initialize
+  ReadAheadSystemDll(L"ExplorerFrame.dll");
+
+  // Load WinTypes.dll for nsOSHelperAppService::GetApplicationDescription
+  ReadAheadSystemDll(L"WinTypes.dll");
+#  endif
 }
 #endif