DevTools: [SSP] consume event if it inserts a new property

Currently, if you click on the selector container, there are two
handlers that conflict with each other. The patch fixes
the conflict.

BUG=413894
R=vsevik, apavlov@chromium.org

Review URL: https://codereview.chromium.org/571653002

git-svn-id: svn://svn.chromium.org/blink/trunk@181963 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/front_end/elements/StylesSidebarPane.js

@@ -1599,8 +1599,10 @@ WebInspector.StylePropertiesSection.prototype = {
     {
         if (this._checkWillCancelEditing() || !this.editable)
             return;
-        if (event.target === this._selectorContainer)
+        if (event.target === this._selectorContainer) {
             this.addNewBlankProperty(0).startEditing();
+            event.consume(true);
+        }
     },
 
     /**
@@ -1697,6 +1699,7 @@ WebInspector.StylePropertiesSection.prototype = {
         }
         this.expand();
         this.addNewBlankProperty().startEditing();
+        event.consume(true)
     },
 
     _handleSelectorClick: function(event)