Introduce a flag to control microtask scope consistency checking

We want to be stricter about checking in the future, so give embedders a
way to disable checking while they fix their microtasks scopes.

BUG=chromium:728583
R=machenbach@chromium.org

Change-Id: I443575bf6820b432def59cbbd4d048b2007573c8
Reviewed-on: https://chromium-review.googlesource.com/522604
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45677}

BUILD.gn

@@ -118,6 +118,10 @@ declare_args() {
   v8_enable_gdbjit = ((v8_current_cpu == "x86" || v8_current_cpu == "x64" ||
                        v8_current_cpu == "x87") && (is_linux || is_mac)) ||
                      (v8_current_cpu == "ppc64" && is_linux)
+
+  # Temporary flag to allow embedders to update their microtasks scopes
+  # while rolling in a new version of V8.
+  v8_check_microtasks_scopes_consistency = ""
 }
 
 # Derived defaults.
@@ -136,6 +140,9 @@ if (v8_enable_trace_maps == "") {
 if (v8_enable_v8_checks == "") {
   v8_enable_v8_checks = is_debug
 }
+if (v8_check_microtasks_scopes_consistency == "") {
+  v8_check_microtasks_scopes_consistency = is_debug || v8_enable_v8_checks
+}
 
 # Specifies if the target build is a simulator build. Comparing target cpu
 # with v8 target cpu to not affect simulator builds for making cross-compile
@@ -277,6 +284,9 @@ config("features") {
   if (v8_enable_concurrent_marking) {
     defines += [ "V8_CONCURRENT_MARKING" ]
   }
+  if (v8_check_microtasks_scopes_consistency) {
+    defines += [ "V8_CHECK_MICROTASKS_SCOPES_CONSISTENCY" ]
+  }
 }
 
 config("toolchain") {

gypfiles/features.gypi

@@ -73,6 +73,9 @@
 
     # Enable/disable JavaScript API accessors.
     'v8_js_accessors%': 0,
+
+    # Temporary flag to allow embedders to update their microtasks scopes.
+    'v8_check_microtasks_scopes_consistency%': 'false',
   },
   'target_defaults': {
     'conditions': [
@@ -118,6 +121,9 @@
       ['dcheck_always_on!=0', {
         'defines': ['DEBUG',],
       }],
+      ['v8_check_microtasks_scopes_consistency=="true"', {
+        'defines': ['V8_CHECK_MICROTASKS_SCOPES_CONSISTENCY',],
+      }],
     ],  # conditions
     'configurations': {
       'DebugBaseCommon': {

gypfiles/standalone.gypi

@@ -43,6 +43,7 @@
     'v8_enable_i18n_support%': 1,
     'v8_deprecation_warnings': 1,
     'v8_imminent_deprecation_warnings': 1,
+    'v8_check_microtasks_scopes_consistency': 'true',
     'msvs_multi_core_compile%': '1',
     'mac_deployment_target%': '10.7',
     'release_extra_cflags%': '',

src/api.cc

@@ -219,8 +219,8 @@ class InternalEscapableScope : public v8::EscapableHandleScope {
       : v8::EscapableHandleScope(reinterpret_cast<v8::Isolate*>(isolate)) {}
 };
 
-
-#ifdef DEBUG
+// TODO(jochen): This should be #ifdef DEBUG
+#ifdef V8_CHECK_MICROTASKS_SCOPES_CONSISTENCY
 void CheckMicrotasksScopesConsistency(i::Isolate* isolate) {
   auto handle_scope_implementer = isolate->handle_scope_implementer();
   if (handle_scope_implementer->microtasks_policy() ==
@@ -259,7 +259,8 @@ class CallDepthScope {
     }
     if (!escaped_) isolate_->handle_scope_implementer()->DecrementCallDepth();
     if (do_callback) isolate_->FireCallCompletedCallback();
-#ifdef DEBUG
+// TODO(jochen): This should be #ifdef DEBUG
+#ifdef V8_CHECK_MICROTASKS_SCOPES_CONSISTENCY
     if (do_callback) CheckMicrotasksScopesConsistency(isolate_);
 #endif
   }