Bug 1639391: Do not call nsWindow::GetAttention for top-level windows being shown during session restore; r=mhowell

When we call nsWindow::Show but Firefox is not foreground, we show the window
and also flash it on the taskbar to get the user's attention.

This is really annoying when restoring a session with `N` windows, as the
user's taskbar ends up with all `N` of them stuck in a flashed state until the
user goes through and manually activates every single window.

There are several ways I thought of to address this, but I think the
simplest one is just to track whether or not we're in the middle of restoring a
session and skip flashing when we are doing so.

Differential Revision: https://phabricator.services.mozilla.com/D76406

widget/windows/nsAppShell.cpp

@@ -12,6 +12,7 @@
 #include "WinTaskbar.h"
 #include "WinMouseScrollHandler.h"
 #include "nsWindowDefs.h"
+#include "nsWindow.h"
 #include "nsString.h"
 #include "WinIMEHandler.h"
 #include "mozilla/widget/AudioSession.h"
@@ -281,33 +282,52 @@ static void InitUIADetection() {
   }
 }
 
+#endif  // defined(ACCESSIBILITY)
+
 NS_IMETHODIMP
 nsAppShell::Observe(nsISupports* aSubject, const char* aTopic,
                     const char16_t* aData) {
-  if (XRE_IsParentProcess() && !strcmp(aTopic, "dll-loaded-main-thread")) {
-    if (a11y::PlatformDisabledState() != a11y::ePlatformIsDisabled &&
-        !gUiaHook) {
-      nsDependentString dllName(aData);
+  if (XRE_IsParentProcess()) {
+    nsCOMPtr<nsIObserverService> obsServ(
+        mozilla::services::GetObserverService());
 
-      if (StringEndsWith(dllName, NS_LITERAL_STRING("uiautomationcore.dll"),
-                         nsCaseInsensitiveStringComparator())) {
-        InitUIADetection();
+#if defined(ACCESSIBILITY)
+    if (!strcmp(aTopic, "dll-loaded-main-thread")) {
+      if (a11y::PlatformDisabledState() != a11y::ePlatformIsDisabled &&
+          !gUiaHook) {
+        nsDependentString dllName(aData);
 
-        // Now that we've handled the observer notification, we can remove it
-        nsCOMPtr<nsIObserverService> obsServ(
-            mozilla::services::GetObserverService());
-        obsServ->RemoveObserver(this, "dll-loaded-main-thread");
+        if (StringEndsWith(dllName, NS_LITERAL_STRING("uiautomationcore.dll"),
+                           nsCaseInsensitiveStringComparator())) {
+          InitUIADetection();
+
+          // Now that we've handled the observer notification, we can remove it
+          obsServ->RemoveObserver(this, "dll-loaded-main-thread");
+        }
       }
+
+      return NS_OK;
+    }
+#endif  // defined(ACCESSIBILITY)
+
+    if (!strcmp(aTopic, "sessionstore-restoring-on-startup")) {
+      nsWindow::SetIsRestoringSession(true);
+      // Now that we've handled the observer notification, we can remove it
+      obsServ->RemoveObserver(this, "sessionstore-restoring-on-startup");
+      return NS_OK;
     }
 
-    return NS_OK;
+    if (!strcmp(aTopic, "sessionstore-windows-restored")) {
+      nsWindow::SetIsRestoringSession(false);
+      // Now that we've handled the observer notification, we can remove it
+      obsServ->RemoveObserver(this, "sessionstore-windows-restored");
+      return NS_OK;
+    }
   }
 
   return nsBaseAppShell::Observe(aSubject, aTopic, aData);
 }
 
-#endif  // defined(ACCESSIBILITY)
-
 nsresult nsAppShell::Init() {
   LSPAnnotate();
 
@@ -374,12 +394,16 @@ nsresult nsAppShell::Init() {
       ScreenHelperWin::RefreshScreens();
     }
 
+    nsCOMPtr<nsIObserverService> obsServ(
+        mozilla::services::GetObserverService());
+
+    obsServ->AddObserver(this, "sessionstore-restoring-on-startup", false);
+    obsServ->AddObserver(this, "sessionstore-windows-restored", false);
+
 #if defined(ACCESSIBILITY)
     if (::GetModuleHandleW(L"uiautomationcore.dll")) {
       InitUIADetection();
     } else {
-      nsCOMPtr<nsIObserverService> obsServ(
-          mozilla::services::GetObserverService());
       obsServ->AddObserver(this, "dll-loaded-main-thread", false);
     }
 #endif  // defined(ACCESSIBILITY)

widget/windows/nsAppShell.h

@@ -40,11 +40,8 @@ class nsAppShell : public nsBaseAppShell {
  protected:
   NS_IMETHOD Run() override;
   NS_IMETHOD Exit() override;
-
-#if defined(ACCESSIBILITY)
   NS_IMETHOD Observe(nsISupports* aSubject, const char* aTopic,
                      const char16_t* aData) override;
-#endif  // defined(ACCESSIBILITY)
 
   virtual void ScheduleNativeEventCallback();
   virtual bool ProcessNextNativeEvent(bool mayWait);

widget/windows/nsWindow.cpp

@@ -274,6 +274,7 @@ LONG nsWindow::sLastClickCount = 0L;
 BYTE nsWindow::sLastMouseButton = 0;
 
 bool nsWindow::sHaveInitializedPrefs = false;
+bool nsWindow::sIsRestoringSession = false;
 
 TriStateBool nsWindow::sHasBogusPopupsDropShadowOnMultiMonitor = TRI_UNKNOWN;
 
@@ -1615,7 +1616,10 @@ void nsWindow::Show(bool bState) {
               ::ShowWindow(mWnd, SW_SHOWNORMAL);
             } else {
               ::ShowWindow(mWnd, SW_SHOWNOACTIVATE);
-              Unused << GetAttention(2);
+              // Don't flicker the window if we're restoring session
+              if (!sIsRestoringSession) {
+                Unused << GetAttention(2);
+              }
             }
             break;
         }

widget/windows/nsWindow.h

@@ -306,6 +306,10 @@ class nsWindow final : public nsWindowBase {
   void SetSmallIcon(HICON aIcon);
   void SetBigIcon(HICON aIcon);
 
+  static void SetIsRestoringSession(const bool aIsRestoringSession) {
+    sIsRestoringSession = aIsRestoringSession;
+  }
+
   /**
    * AssociateDefaultIMC() associates or disassociates the default IMC for
    * the window.
@@ -621,6 +625,7 @@ class nsWindow final : public nsWindowBase {
   static bool sJustGotActivate;
   static bool sIsInMouseCapture;
   static bool sHaveInitializedPrefs;
+  static bool sIsRestoringSession;
 
   PlatformCompositorWidgetDelegate* mCompositorWidgetDelegate;