DevTools: Fix timeline overview window selection

The window selection is shown in a left corner when drag was initiated on a marker.

R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/211343003

git-svn-id: svn://svn.chromium.org/blink/trunk@169954 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/front_end/OverviewGrid.js

@@ -252,8 +252,8 @@ WebInspector.OverviewGrid.Window.prototype = {
     {
         if (!this._enabled)
             return false;
-        this._offsetLeft = event.pageX - event.offsetX;
-        var position = event.pageX - this._offsetLeft;
+        this._offsetLeft = this._parentElement.totalOffsetLeft();
+        var position = event.x - this._offsetLeft;
         this._overviewWindowSelector = new WebInspector.OverviewGrid.WindowSelector(this._parentElement, position);
         return true;
     },
@@ -263,7 +263,7 @@ WebInspector.OverviewGrid.Window.prototype = {
      */
     _windowSelectorDragging: function(event)
     {
-        this._overviewWindowSelector._updatePosition(event.pageX - this._offsetLeft);
+        this._overviewWindowSelector._updatePosition(event.x - this._offsetLeft);
         event.preventDefault();
     },
 
@@ -272,7 +272,7 @@ WebInspector.OverviewGrid.Window.prototype = {
      */
     _endWindowSelectorDragging: function(event)
     {
-        var window = this._overviewWindowSelector._close(event.pageX - this._offsetLeft);
+        var window = this._overviewWindowSelector._close(event.x - this._offsetLeft);
         delete this._overviewWindowSelector;
         if (window.end === window.start) { // Click, not drag.
             var middle = window.end;