[debug] introduce precise binary 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/debug/debug-interface.h"
@@ skipping 17 matching lines @@
 struct CoverageScript {
   // Initialize top-level function in case it has been garbage-collected.
   CoverageScript(Isolate* isolate, Handle<Script> s) : script(s) {}
   Handle<Script> script;
   // Functions are sorted by start position, from outer to inner function.
   std::vector<CoverageFunction> functions;
 };
 
 class Coverage : public std::vector<CoverageScript> {
  public:
-  // Allocate a new Coverage object and populate with result.
-  // The ownership is transferred to the caller.
-  static Coverage* Collect(Isolate* isolate, bool reset_count);
+  // Collecting precise coverage only works if the modes kPreciseCount or
+  // kPreciseBinary is selected. The invocation count is reset on collection.
+  // In case of kPreciseCount, an updated count since last collection is
+  // returned. In case of kPreciseBinary, a count of 1 is returned if a
+  // function has been executed for the first time since last collection.
+  static Coverage* CollectPrecise(Isolate* isolate);
+  // Collecting best effort coverage always works, but may be imprecise
+  // depending on selected mode. The invocation count is not reset.
+  static Coverage* CollectBestEffort(Isolate* isolate);
 
   // Select code coverage mode.
   static void SelectMode(Isolate* isolate, debug::Coverage::Mode mode);
 
  private:
+  static Coverage* Collect(Isolate* isolate,
+                           v8::debug::Coverage::Mode collectionMode);
+
   Coverage() {}
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_COVERAGE_H_