Bug 1043920 - Reader mode (ambient light detection) prevents device from sleeping r=margaret

mobile/android/chrome/content/aboutReader.js

@@ -61,6 +61,8 @@ let AboutReader = function(doc, win) {
   win.addEventListener("popstate", this, false);
   win.addEventListener("resize", this, false);
 
+  doc.addEventListener("visibilitychange", this, false);
+
   this._setupAllDropdowns();
   this._setupButton("toggle-button", this._onReaderToggle.bind(this));
   this._setupButton("share-button", this._onShare.bind(this));
@@ -271,6 +273,10 @@ AboutReader.prototype = {
         this._handleDeviceLight(aEvent.value);
         break;
 
+      case "visibilitychange":
+        this._handleVisibilityChange();
+        break;
+
       case "unload":
         Services.obs.removeObserver(this, "Reader:Add");
         Services.obs.removeObserver(this, "Reader:Remove");
@@ -399,6 +405,29 @@ AboutReader.prototype = {
     this._totalLux -= oldLux;
   },
 
+  _handleVisibilityChange: function Reader_handleVisibilityChange() {
+    let colorScheme = Services.prefs.getCharPref("reader.color_scheme");
+    if (colorScheme != "auto") {
+      return;
+    }
+
+    // Turn off the ambient light sensor if the page is hidden
+    this._enableAmbientLighting(!this._doc.hidden);
+  },
+
+  // Setup or teardown the ambient light tracking system.
+  _enableAmbientLighting: function Reader_enableAmbientLighting(enable) {
+    if (enable) {
+      this._win.addEventListener("devicelight", this, false);
+      this._luxValues = [];
+      this._totalLux = 0;
+    } else {
+      this._win.removeEventListener("devicelight", this, false);
+      delete this._luxValues;
+      delete this._totalLux;
+    }
+  },
+
   _updateColorScheme: function Reader_updateColorScheme(luxValue) {
     // Upper bound value for "dark" color scheme beyond which it changes to "light".
     let upperBoundDark = 50;
@@ -419,7 +448,8 @@ AboutReader.prototype = {
   },
 
   _setColorScheme: function Reader_setColorScheme(newColorScheme) {
-    if (this._colorScheme === newColorScheme)
+    // "auto" is not a real color scheme
+    if (this._colorScheme === newColorScheme || newColorScheme === "auto")
       return;
 
     let bodyClasses = this._doc.body.classList;
@@ -434,16 +464,8 @@ AboutReader.prototype = {
   // Pref values include "dark", "light", and "auto", which automatically switches
   // between light and dark color schemes based on the ambient light level.
   _setColorSchemePref: function Reader_setColorSchemePref(colorSchemePref) {
-    if (colorSchemePref === "auto") {
-      this._win.addEventListener("devicelight", this, false);
-      this._luxValues = [];
-      this._totalLux = 0;
-    } else {
-      this._win.removeEventListener("devicelight", this, false);
-      this._setColorScheme(colorSchemePref);
-      delete this._luxValues;
-      delete this._totalLux;
-    }
+    this._enableAmbientLighting(colorSchemePref === "auto");
+    this._setColorScheme(colorSchemePref);
 
     Services.prefs.setCharPref("reader.color_scheme", colorSchemePref);
   },