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

test/mjsunit/code-coverage-precise.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 precise code coverage.
 
 function GetCoverage(source) {
   for (var script of %DebugCollectCoverage()) {
@@ skipping 52 matching lines @@
 
 // This does not happen with precise coverage enabled.
 %DebugTogglePreciseCoverage(true);
 
 TestCoverage(
 "call an IIFE",
 `
 (function f() {})();
 `,
 `
-[([function f() {}](f:1))();](anonymous:1)
+[([function f() {}](f:1))();](:1)
 `
 );
 
 TestCoverage(
 "call locally allocated function",
 `
 for (var i = 0; i < 10; i++) {
   let f = () => 1;
   i += f();
 }
 `,
 `
 [for (var i = 0; i < 10; i++) {
   let f = [() => 1](f:5);
   i += f();
-}](anonymous:1)
+}](:1)
 `
 );
 
 %DebugTogglePreciseCoverage(false);