code review by hf: merge zhangzhen code to fixes home floor bugs

@@ -2185,11 +2185,23 @@ var $searchBox = $('.search-box'),
     $box = $('.box'),
     $indexSearch = $('.index-search'),
     $indexLogo = $('.index-logo'),
-    $channelLink = $('.index-channel a');
+    $channelLink = $('.index-channel a'),
+    $win = $(window),
+    $doc = $(document),
+    $appFloatLayer = $('#float-layer-app');
 
 var $search = $searchBox.children('input[type="text"]'),
-        $cancelSearch = $box.children('.no-search'),
-        $searchIcon = $searchBox.children('.search-icon');
+    $cancelSearch = $box.children('.no-search'),
+    $searchIcon = $searchBox.children('.search-icon');
+
+// variables for calculate the app download layer position
+var layerInit = false,
+    windowViewHeight = 0,
+    layerContentHeight = $appFloatLayer.height(),
+    layerPaddingTop = parseInt($appFloatLayer.css('padding-top')),
+    layerPaddingBottom = parseInt($appFloatLayer.css('padding-bottom')),
+    layerHeight = layerContentHeight + layerPaddingTop + layerPaddingBottom,
+    layerNewPos;
 
 require("js/common");
 
@@ -2245,6 +2257,43 @@ $channelLink.on('touchstart', function() {
     });
 });
 
+
+function updateLayerPosition() {
+    var winHeight = window.innerHeight,
+        bodyHeight = $doc.height(),
+        scrollTopPosition = $win.scrollTop();
+
+    if (layerInit) {
+
+        //keyboard is shown
+        if (windowViewHeight - winHeight > 200) {
+            if (scrollTopPosition + windowViewHeight + layerHeight >= bodyHeight) {
+                layerNewPos = 0;
+            } else {
+                layerNewPos = bodyHeight - windowViewHeight - scrollTopPosition - layerHeight;
+            }
+        } else {
+            layerNewPos = bodyHeight - winHeight - scrollTopPosition;
+        }
+
+    } else {
+        windowViewHeight = winHeight;
+        layerNewPos = bodyHeight - winHeight - scrollTopPosition + layerHeight;
+        layerInit = true;
+    }
+
+    $appFloatLayer.css({
+        position: 'relative',
+        bottom: layerNewPos + 'px'
+    });
+}
+
+$(window).scroll(function() {
+    window.requestAnimationFrame(updateLayerPosition);
+});
+
+$doc.on('ready', updateLayerPosition);
+
 });
 define("js/passport/entry", ["jquery"], function(require, exports, module){
 /**