[debug] introduce precise binary code coverage.

src/debug/debug-coverage.h

Index: src/debug/debug-coverage.h
diff --git a/src/debug/debug-coverage.h b/src/debug/debug-coverage.h
index 02c89e63f9ddff01e72dc7f382bcca90cb9abb40..f37b8f37440fe7697054ecca2c8655bc8c598ed0 100644
--- a/src/debug/debug-coverage.h
+++ b/src/debug/debug-coverage.h
@@ -35,14 +35,22 @@ struct CoverageScript {
 
 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, bool reset_count);
+
   Coverage() {}
 };