[debugger] implement per-function code coverage.

src/debug/debug-coverage.h

+// 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.
+
+#ifndef V8_DEBUG_DEBUG_COVERAGE_H_
+#define V8_DEBUG_DEBUG_COVERAGE_H_
+
+#include <vector>
+
+#include "src/allocation.h"
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace internal {
+
+// Forward declaration.
+class Isolate;
+
+class Coverage : public AllStatic {
+ public:
+  struct RangeEntry {
+    int end_position;
+    uint32_t count;
+  };
+
+  struct ScriptData {
+    ScriptData(int s, std::vector<RangeEntry> e)
+        : script_id(s), entries(std::move(e)) {}
+    int script_id;
+    std::vector<RangeEntry> entries;
+  };
+
+  static std::vector<ScriptData> Collect(Isolate* isolate);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_DEBUG_DEBUG_COVERAGE_H_