update one-line docs for svg, gl, audio

BUG=
R=vsm@google.com

Review URL: https://codereview.chromium.org//1163163004

sdk/lib/svg/dartium/svg_dartium.dart

@@ -1,3 +1,11 @@
+/**
+ * Scalable Vector Graphics:
+ * Two-dimensional vector graphics with support for events and animation.
+ *
+ * For details about the features and syntax of SVG, a W3C standard,
+ * refer to the
+ * [Scalable Vector Graphics Specification](http://www.w3.org/TR/SVG/).
+ */
 library dart.dom.svg;
 
 import 'dart:async';

sdk/lib/web_audio/dartium/web_audio_dartium.dart

@@ -1,3 +1,6 @@
+/**
+ * High-fidelity audio programming in the browser.
+ */
 library dart.dom.web_audio;
 
 import 'dart:async';

sdk/lib/web_gl/dartium/web_gl_dartium.dart

@@ -1,3 +1,6 @@
+/**
+ * 3D programming in the browser.
+ */
 library dart.dom.web_gl;
 
 import 'dart:async';