Expand overloaded methods and optional parameters in the html library.

tools/dom/idl/dart/dart.idl

 // This file introduces / supplements and forces Dart declarations.
 
 [Supplemental,
  Constructor]
 interface AudioContext {
   // TODO(ager): Auto-generate this custom method when the info about retaining
   // typed arrays is in the IDL.
   [Custom] void decodeAudioData(ArrayBuffer audioData, AudioBufferCallback successCallback, AudioBufferCallback errorCallback);
 };
 
@@ skipping 135 matching lines @@
   [Suppressed, StrictTypeChecking, Custom] void getRenderbufferParameter();
 
   [Custom] any getShaderParameter(WebGLShader shader, unsigned long pname);
   [Suppressed, StrictTypeChecking, Custom] void getShaderParameter();
 
   // TBD
   // void glGetShaderPrecisionFormat (GLenum shadertype, GLenum precisiontype, GLint* range, GLint* precision);
 
   [Custom] any getExtension(DOMString name);
   [Suppressed, StrictTypeChecking, Custom] void getExtension(DOMString name);
-  [Custom] DOMString[] getSupportedExtensions();
   [Suppressed, StrictTypeChecking, Custom] void getSupportedExtensions();
 
   [Custom] any getTexParameter(unsigned long target, unsigned long pname);
   [Suppressed, StrictTypeChecking, Custom] void getTexParameter();
 
   [Custom] any getUniform(WebGLProgram program, WebGLUniformLocation location);
   [Suppressed, StrictTypeChecking, Custom] void getUniform();
 
   [Custom] any getVertexAttrib(unsigned long index, unsigned long pname);
   [Suppressed, StrictTypeChecking, Custom] void getVertexAttrib();
@@ skipping 145 matching lines @@
   [Custom] void reload();
 
   // URI decomposition attributes
   [CustomSetter] attribute DOMString protocol;
   [CustomSetter] attribute DOMString host;
   [CustomSetter] attribute DOMString hostname;
   [CustomSetter] attribute DOMString port;
   [CustomSetter] attribute DOMString pathname;
   [CustomSetter] attribute DOMString search;
   [CustomSetter] attribute DOMString hash;
-};
+};