Remove obsolete try/catch from ObjectIsPromise().

Review URL: https://codereview.chromium.org/1367123003

Cr-Commit-Position: refs/heads/master@{#30966}

src/debug/mirrors.js

@@ -107,16 +107,9 @@ function ClearMirrorCache(value) {
 }
 
 
-// Wrapper to check whether an object is a Promise.  The call may not work
-// if promises are not enabled.
-// TODO(yangguo): remove try-catch once promises are enabled by default.
 function ObjectIsPromise(value) {
-  try {
-    return IS_SPEC_OBJECT(value) &&
-           !IS_UNDEFINED(%DebugGetProperty(value, promiseStatusSymbol));
-  } catch (e) {
-    return false;
-  }
+  return IS_SPEC_OBJECT(value) &&
+         !IS_UNDEFINED(%DebugGetProperty(value, promiseStatusSymbol));
 }