[debug] refactor code coverage to use enum for mode.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 0d6494604edb8956bb48ac014abf51a2d995fd2e..d272a77db5a269f3dddf91d87878980c3a564315 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -14,6 +14,7 @@
 #include "src/builtins/builtins.h"
 #include "src/contexts.h"
 #include "src/date.h"
+#include "src/debug/debug-interface.h"
 #include "src/execution.h"
 #include "src/frames.h"
 #include "src/futex-emulation.h"
@@ -422,6 +423,8 @@ typedef List<HeapObject*> DebugObjectCache;
   V(bool, formatting_stack_trace, false)                                      \
   /* Perform side effect checks on function call and API callbacks. */        \
   V(bool, needs_side_effect_check, false)                                     \
+  /* Current code coverage mode */                                            \
+  V(debug::Coverage::Mode, code_coverage_mode, debug::Coverage::kBestEffort)  \
   ISOLATE_INIT_SIMULATOR_LIST(V)
 
 #define THREAD_LOCAL_TOP_ACCESSOR(type, name)                        \
@@ -975,7 +978,14 @@ class Isolate {
 
   bool NeedsSourcePositionsForProfiling() const;
 
-  bool IsCodeCoverageEnabled();
+  bool is_best_effort_code_coverage() const {
+    return code_coverage_mode() == debug::Coverage::kBestEffort;
+  }
+
+  bool is_precise_count_code_coverage() const {
+    return code_coverage_mode() == debug::Coverage::kPreciseCount;
+  }
+
   void SetCodeCoverageList(Object* value);
 
   double time_millis_since_init() {