Mark onvisibilitychange & visibilityState partial

This change marks support for the onvisibilitychange event handler and
document.visibilityState property a partial_implementation:true for
Safari (due the fact that Safari apparently doesn’t fire visibilitychange
as expected when visibilityState transitions to "hidden").

Author: sideshowbarker

api/Document.json

@@ -7671,10 +7671,14 @@
               "notes": "Doesn't fire the <code>visibilitychange</code> event when the browser window is minimized, nor when <code>hidden</code> is set to true."
             },
             "safari": {
-              "version_added": "7"
+              "version_added": "7",
+              "partial_implementation": true,
+              "notes": "Doesn't fire the <code>visibilitychange</code> event when <code>document.visibilityState</code> transitions to <code>hidden</code>, so also include code to check for the <code>pagehide</code> event (which does fire for that case in all current browsers). See WebKit bugs <a href='https://webkit.org/b/116769'>116769</a>, <a href='https://webkit.org/b/151234'>151234</a>, <a href='https://webkit.org/b/151610'>151610</a>, and <a href='https://webkit.org/b/194897'>194897</a>."
             },
             "safari_ios": {
-              "version_added": "7"
+              "version_added": "7",
+              "partial_implementation": true,
+              "notes": "Doesn't fire the <code>visibilitychange</code> event when <code>document.visibilityState</code> transitions to <code>hidden</code>, so also include code to check for the <code>pagehide</code> event (which does fire for that case in all current browsers). See WebKit bugs <a href='https://webkit.org/b/116769'>116769</a>, <a href='https://webkit.org/b/151234'>151234</a>, <a href='https://webkit.org/b/151610'>151610</a>, and <a href='https://webkit.org/b/194897'>194897</a>."
             },
             "samsunginternet_android": {
               "version_added": "2.0"
@@ -10919,10 +10923,14 @@
               "notes": "Doesn't fire the <code>visibilitychange</code> event when the browser window is minimized, nor when <code>hidden</code> is set to true."
             },
             "safari": {
-              "version_added": "7"
+              "version_added": "7",
+              "partial_implementation": true,
+              "notes": "Doesn't fire the <code>visibilitychange</code> event when <code>document.visibilityState</code> transitions to <code>hidden</code>, so also include code to check for the <code>pagehide</code> event (which does fire for that case in all current browsers). See WebKit bugs <a href='https://webkit.org/b/116769'>116769</a>, <a href='https://webkit.org/b/151234'>151234</a>, <a href='https://webkit.org/b/151610'>151610</a>, and <a href='https://webkit.org/b/194897'>194897</a>."
             },
             "safari_ios": {
-              "version_added": "7"
+              "version_added": "7",
+              "partial_implementation": true,
+              "notes": "Doesn't fire the <code>visibilitychange</code> event when <code>document.visibilityState</code> transitions to <code>hidden</code>, so also include code to check for the <code>pagehide</code> event (which does fire for that case in all current browsers). See WebKit bugs <a href='https://webkit.org/b/116769'>116769</a>, <a href='https://webkit.org/b/151234'>151234</a>, <a href='https://webkit.org/b/151610'>151610</a>, and <a href='https://webkit.org/b/194897'>194897</a>."
             },
             "samsunginternet_android": [
               {