Bug 1773118 - Fix transition from fullscreen to maximized. r=stransky

We don't call MakeFullScreen(false), causing weirdness. This is needed even
with the next patch because otherwise other things like grabbing the tabbar
cause the same kind of weirdness.

Differential Revision: https://phabricator.services.mozilla.com/D148340

Author: emilio

widget/gtk/nsWindow.cpp

@@ -2493,13 +2493,26 @@ void nsWindow::SetSizeMode(nsSizeMode aMode) {
   // Save the requested state.
   mSizeMode = aMode;
 
-  // return if there's no shell or our current state is the same as
-  // the mode we were just set to.
-  if (!mShell || mSizeState == mSizeMode) {
+  // Return if there's no shell or our current state is the same as the mode we
+  // were just set to.
+  if (!mShell || mSizeState == aMode) {
     LOG("    already set");
     return;
   }
 
+  if (mSizeState == nsSizeMode_Fullscreen) {
+    LOG("    unfullscreening");
+    MakeFullScreen(false);
+    // NOTE: Fullscreen restoration changes mSizeMode to the state before
+    // fullscreen, but we might need to still transition to aMode.
+    mSizeState = mSizeMode;
+    mSizeMode = aMode;
+    if (mSizeState == aMode) {
+      LOG("    restored to desired state");
+      return;
+    }
+  }
+
   switch (aMode) {
     case nsSizeMode_Maximized:
       LOG("    set maximized");
@@ -2513,20 +2526,18 @@ void nsWindow::SetSizeMode(nsSizeMode aMode) {
       LOG("    set fullscreen");
       MakeFullScreen(true);
       break;
-
     default:
+      MOZ_FALLTHROUGH_ASSERT("Unknown size mode");
+    case nsSizeMode_Normal:
       LOG("    set normal");
       // nsSizeMode_Normal, really.
       if (mSizeState == nsSizeMode_Minimized) {
         gtk_window_deiconify(GTK_WINDOW(mShell));
       } else if (mSizeState == nsSizeMode_Maximized) {
         gtk_window_unmaximize(GTK_WINDOW(mShell));
-      } else if (mSizeState == nsSizeMode_Fullscreen) {
-        MakeFullScreen(false);
       }
       break;
   }
-
   mSizeState = mSizeMode;
 }
 
@@ -7098,7 +7109,9 @@ nsresult nsWindow::MakeFullScreen(bool aFullScreen) {
   }
 
   if (aFullScreen) {
-    if (mSizeMode != nsSizeMode_Fullscreen) mLastSizeMode = mSizeMode;
+    if (mSizeMode != nsSizeMode_Fullscreen) {
+      mLastSizeMode = mSizeMode;
+    }
 
     mSizeMode = nsSizeMode_Fullscreen;