In Isolate::Throw, call PredictExceptionCatcher only if necessary.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 4c3f8940cd2fd00719fcfcd6a3a0212ed8208f98..f250e49e165825e4aa62acf7dbdd318e2b64f75d 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1143,20 +1143,21 @@ Object* Isolate::Throw(Object* exception, MessageLocation* location) {
       // embedder didn't specify a custom uncaught exception callback,
       // or if the custom callback determined that V8 should abort, then
       // abort.
-      CatchType prediction = PredictExceptionCatcher();
-      if (FLAG_abort_on_uncaught_exception &&
-          (prediction == NOT_CAUGHT || prediction == CAUGHT_BY_EXTERNAL) &&
-          (!abort_on_uncaught_exception_callback_ ||
-           abort_on_uncaught_exception_callback_(
-               reinterpret_cast<v8::Isolate*>(this)))) {
-        // Prevent endless recursion.
-        FLAG_abort_on_uncaught_exception = false;
-        // This flag is intended for use by JavaScript developers, so
-        // print a user-friendly stack trace (not an internal one).
-        PrintF(stderr, "%s\n\nFROM\n",
-               MessageHandler::GetLocalizedMessage(this, message_obj).get());
-        PrintCurrentStackTrace(stderr);
-        base::OS::Abort();
+      if (FLAG_abort_on_uncaught_exception) {
+        CatchType prediction = PredictExceptionCatcher();
+        if ((prediction == NOT_CAUGHT || prediction == CAUGHT_BY_EXTERNAL) &&
+            (!abort_on_uncaught_exception_callback_ ||
+             abort_on_uncaught_exception_callback_(
+                 reinterpret_cast<v8::Isolate*>(this)))) {
+          // Prevent endless recursion.
+          FLAG_abort_on_uncaught_exception = false;
+          // This flag is intended for use by JavaScript developers, so
+          // print a user-friendly stack trace (not an internal one).
+          PrintF(stderr, "%s\n\nFROM\n",
+                 MessageHandler::GetLocalizedMessage(this, message_obj).get());
+          PrintCurrentStackTrace(stderr);
+          base::OS::Abort();
+        }
       }
     }
   }