Bug 1319764 - Ensure Gtk window unmap workaround is actually used. r=karlt

We were miscounting the number of manual configure events which we
needed to send gtk as the workaround for bug 1225044, causing it not
to work in some cases. This is because configure events can come from
more sources than were counting.

Decrement mPendingConfigures only as far as zero, like
configure_request_count in gtk_window_configure_event().

MozReview-Commit-ID: GxpR2Zozxor

--HG--
extra : rebase_source : 9d02c4d019d8bea7a07c20fb1435d2f677ae6e28

widget/gtk/nsWindow.cpp

@@ -2401,7 +2401,9 @@ nsWindow::OnConfigureEvent(GtkWidget *aWidget, GdkEventConfigure *aEvent)
     LOG(("configure event [%p] %d %d %d %d\n", (void *)this,
          aEvent->x, aEvent->y, aEvent->width, aEvent->height));
 
-    mPendingConfigures--;
+    if (mPendingConfigures > 0) {
+        mPendingConfigures--;
+    }
 
     LayoutDeviceIntRect screenBounds = GetScreenBounds();
 
@@ -4212,7 +4214,7 @@ nsWindow::NativeShow(bool aAction)
                 event.height = allocation.height;
 
                 auto shellClass = GTK_WIDGET_GET_CLASS(mShell);
-                for (int i = 0; i < mPendingConfigures; i++) {
+                for (unsigned int i = 0; i < mPendingConfigures; i++) {
                     Unused << shellClass->configure_event(mShell, &event);
                 }
                 mPendingConfigures = 0;

widget/gtk/nsWindow.h

@@ -469,7 +469,7 @@ private:
 
     // Upper bound on pending ConfigureNotify events to be dispatched to the
     // window. See bug 1225044.
-    int mPendingConfigures;
+    unsigned int mPendingConfigures;
 
 #ifdef ACCESSIBILITY
     RefPtr<mozilla::a11y::Accessible> mRootAccessible;