[api] Minor improvement to documentation for kNonMasking.

BUG=

Review-Url: https://codereview.chromium.org/2302133003
Cr-Commit-Position: refs/heads/master@{#39137}

include/v8.h

@@ -4992,20 +4992,19 @@ class V8_EXPORT FunctionTemplate : public Template {
   friend class ObjectTemplate;
 };
 
-
 enum class PropertyHandlerFlags {
   kNone = 0,
   // See ALL_CAN_READ above.
   kAllCanRead = 1,
   // Will not call into interceptor for properties on the receiver or prototype
-  // chain.  Currently only valid for named interceptors.
+  // chain, i.e., only call into interceptor for properties that do not exist.
+  // Currently only valid for named interceptors.
   kNonMasking = 1 << 1,
   // Will not call into interceptor for symbol lookup.  Only meaningful for
   // named interceptors.
   kOnlyInterceptStrings = 1 << 2,
 };
 
-
 struct NamedPropertyHandlerConfiguration {
   NamedPropertyHandlerConfiguration(
       /** Note: getter is required **/

test/cctest/test-api-interceptors.cc

@@ -4338,6 +4338,9 @@ THREADED_TEST(NonMaskingInterceptorOwnProperty) {
   ExpectInt32("obj.whatever", 239);
 
   CompileRun("obj.whatever = 4;");
+
+  // obj.whatever exists, thus it is not affected by the non-masking
+  // interceptor.
   ExpectInt32("obj.whatever", 4);
 
   CompileRun("delete obj.whatever;");