[debug] introduce precise binary code coverage.

src/runtime/runtime-debug.cc

 // Copyright 2014 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.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/compiler.h"
 #include "src/debug/debug-coverage.h"
 #include "src/debug/debug-evaluate.h"
@@ skipping 1886 matching lines @@
 
 RUNTIME_FUNCTION(Runtime_DebugBreakInOptimizedCode) {
   UNIMPLEMENTED();
   return NULL;
 }
 
 RUNTIME_FUNCTION(Runtime_DebugCollectCoverage) {
   HandleScope scope(isolate);
   DCHECK_EQ(0, args.length());
   // Collect coverage data.
-  std::unique_ptr<Coverage> coverage(Coverage::Collect(isolate, false));
+  std::unique_ptr<Coverage> coverage;
+  if (isolate->is_best_effort_code_coverage()) {
+    coverage.reset(Coverage::CollectBestEffort(isolate));
+  } else {
+    coverage.reset(Coverage::CollectPrecise(isolate));
+  }
   Factory* factory = isolate->factory();
   // Turn the returned data structure into JavaScript.
   // Create an array of scripts.
   int num_scripts = static_cast<int>(coverage->size());
   // Prepare property keys.
   Handle<FixedArray> scripts_array = factory->NewFixedArray(num_scripts);
   Handle<String> script_string = factory->NewStringFromStaticChars("script");
   Handle<String> start_string = factory->NewStringFromStaticChars("start");
   Handle<String> end_string = factory->NewStringFromStaticChars("end");
   Handle<String> count_string = factory->NewStringFromStaticChars("count");
@@ skipping 27 matching lines @@
 RUNTIME_FUNCTION(Runtime_DebugTogglePreciseCoverage) {
   SealHandleScope shs(isolate);
   CONVERT_BOOLEAN_ARG_CHECKED(enable, 0);
   Coverage::SelectMode(isolate, enable ? debug::Coverage::kPreciseCount
                                        : debug::Coverage::kBestEffort);
   return isolate->heap()->undefined_value();
 }
 
 }  // namespace internal
 }  // namespace v8