Use IDL default argument value for Range.collapse()'s toStart argument

Replace the existing [Default=Undefined] extended attribute, which since
undefined coerces to false means the same thing, with the actual default
value that's in the specification.

BUG=258153

Review URL: https://codereview.chromium.org/356103003

git-svn-id: svn://svn.chromium.org/blink/trunk@177235 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/third_party/WebKit/Source/core/dom/Range.idl b/third_party/WebKit/Source/core/dom/Range.idl
index a19ffa9c7..afc72678 100644
--- a/third_party/WebKit/Source/core/dom/Range.idl
+++ b/third_party/WebKit/Source/core/dom/Range.idl
@@ -38,7 +38,7 @@
     [RaisesException] void setStartAfter(Node refNode);
     [RaisesException] void setEndBefore(Node refNode);
     [RaisesException] void setEndAfter(Node refNode);
-    void collapse([Default=Undefined] optional boolean toStart);
+    void collapse(optional boolean toStart = false);
     [RaisesException] void selectNode(Node refNode);
     [RaisesException] void selectNodeContents(Node refNode);