[debugger] implement inspector-facing API for code coverage.

test/mjsunit/code-coverage-ad-hoc.js

 // Copyright 2017 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax --no-always-opt
 
 // Test code coverage without explicitly activating it upfront.
 
 function GetCoverage(source) {
   for (var script of %DebugCollectCoverage()) {
@@ skipping 27 matching lines @@
 TestCoverage(
 "call simple function twice",
 `
 function f() {}
 f();
 f();
 `,
 `
 [[function f() {}](f:2)
 f();
-f();](anonymous:1)
+f();](:1)
 `
 );
 
 TestCoverage(
 "call arrow function twice",
 `
 var f = () => 1;
 f();
 f();
 `,
 `
 [var f = [() => 1](f:2);
 f();
-f();](anonymous:1)
+f();](:1)
 `
 );
 
 TestCoverage(
 "call nested function",
 `
 function f() {
   function g() {}
   g();
   g();
 }
 f();
 f();
 `,
 `
 [[function f() {
   [function g() {}](g:4)
   g();
   g();
 }](f:2)
 f();
-f();](anonymous:1)
+f();](:1)
 
 `
 );
 
 TestCoverage(
 "call recursive function",
 `
 function fib(x) {
   if (x < 2) return 1;
   return fib(x-1) + fib(x-2);
 }
 fib(5);
 `,
 `
 [[function fib(x) {
   if (x < 2) return 1;
   return fib(x-1) + fib(x-2);
 }](fib:15)
-fib(5);](anonymous:1)
+fib(5);](:1)
 `
 );