Bug 1448208: Use CheckedInt for overflow check in nsWindowWatcher::SizeOpenedWindow. r=froydnj

--HG--
extra : rebase_source : 5781b2086ee7af0b211fb28d2fda02f433ecbbca

toolkit/components/windowcreator/test/mochitest.ini

@@ -9,6 +9,5 @@ skip-if = (toolkit == "cocoa" && e10s) # bug 1252223
 [test_private_window_from_content.html]
 [test_window_open_position_constraint.html]
 skip-if = toolkit == 'android'
-fail-if = (os == "win" && ccov) # bug 1421715
 [test_window_open_units.html]
 skip-if = toolkit == 'android'

toolkit/components/windowwatcher/nsWindowWatcher.cpp

@@ -59,6 +59,7 @@
 #include "nsIPrefBranch.h"
 #include "nsIPrefService.h"
 #include "nsSandboxFlags.h"
+#include "mozilla/CheckedInt.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/Storage.h"
@@ -2368,19 +2369,26 @@ nsWindowWatcher::SizeOpenedWindow(nsIDocShellTreeOwner* aTreeOwner,
         }
       }
 
-      if (left + winWidth > screenLeft + screenWidth ||
-          left + winWidth < left) {
+      CheckedInt<decltype(left)> leftPlusWinWidth = left;
+      leftPlusWinWidth += winWidth;
+      if (!leftPlusWinWidth.isValid() ||
+          leftPlusWinWidth.value() > screenLeft + screenWidth) {
         left = screenLeft + screenWidth - winWidth;
       }
       if (left < screenLeft) {
         left = screenLeft;
       }
-      if (top + winHeight > screenTop + screenHeight || top + winHeight < top) {
+
+      CheckedInt<decltype(top)> topPlusWinHeight = top;
+      topPlusWinHeight += winHeight;
+      if (!topPlusWinHeight.isValid() ||
+          topPlusWinHeight.value() > screenTop + screenHeight) {
         top = screenTop + screenHeight - winHeight;
       }
       if (top < screenTop) {
         top = screenTop;
       }
+
       if (top != oldTop || left != oldLeft) {
         positionSpecified = true;
       }