Check visibility state in algorithms that fire events (#140)

The requirement to only fire events on documents whose visibility state is
"visible" was already in the normative Security and Privacy section, but it
was not integrated into the algorithms that fire said events.

Related to #33.

index.bs

@@ -373,13 +373,14 @@ Note: Implementations must take [[#automation]] into account to determine whethe
 <div algorithm="deviceorientation firing steps">
 Whenever a <a>significant change in orientation</a> occurs, the user agent must execute the following steps on a <a for="/">navigable</a>'s <a for="navigable">active window</a> <var>window</var>:
 
+  1. Let <var>document</var> be <var>window</var>'s <a>associated Document</a>.
+  1. If <var>document</var>'s <a>visibility state</a> is not "<code>visible</code>", return.
   1. If the implementation cannot provide <a>relative orientation</a> or the resulting <a>absolute orientation</a> data is more accurate:
     1. Let <var>absolute</var> be true.
     1. Let <var>policies</var> be « "<a data-lt="accelerometer-feature"><code>accelerometer</code></a>", "<a data-lt="gyroscope-feature"><code>gyroscope</code></a>", "<a data-lt="magnetometer-feature"><code>magnetometer</code></a>" ».
   1. Otherwise:
     1. Let <var>absolute</var> be false.
     1. Let <var>policies</var> be « "<a data-lt="accelerometer-feature"><code>accelerometer</code></a>", "<a data-lt="gyroscope-feature"><code>gyroscope</code></a>" ».
-  1. Let <var>document</var> be <var>window</var>'s <a>associated Document</a>.
   1. <a for="list">For each</a> <var>policy</var> of <var>policies</var>:
       1. If <var>document</var> is not <a>allowed to use</a> the <a>policy-controlled feature</a> named <var>policy</var>, return.
   1. Invoke <a>fire an orientation event</a> with <a event for="Window"><code>deviceorientation</code></a>, <var>window</var>, and <var>absolute</var>.
@@ -558,6 +559,7 @@ The <dfn method for="DeviceMotionEvent">requestPermission()</dfn> method steps a
 At an <a>implementation-defined</a> interval <var>interval</var>, the user agent must execute the following steps on a <a for="/">navigable</a>'s <a for="navigable">active window</a> <var>window</var>:
 
   1. Let <var>document</var> be <var>window</var>'s <a>associated Document</a>.
+  1. If <var>document</var>'s <a>visibility state</a> is not "<code>visible</code>", return.
   1. <a for="list">For each</a> <var>policy</var> of « "<a data-lt="accelerometer-feature"><code>accelerometer</code></a>", "<a data-lt="gyroscope-feature"><code>gyroscope</code></a>" »:
       1. If <var>document</var> is not <a>allowed to use</a> the <a>policy-controlled feature</a> named <var>policy</var>, return.
   1. Let <var>topLevelTraversable</var> be <var>window</var>'s <a for=Window>navigable</a>'s <a for=navigable>top-level traversable</a>.