By default, don't clear exceptions in JSEntryStub

src/flag-definitions.h

 // Copyright 2012 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.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 750 matching lines @@
 DEFINE_BOOL(verify_heap, false, "verify heap pointers before and after GC")
 #endif
 DEFINE_BOOL(move_object_start, true, "enable moving of object starts")
 DEFINE_BOOL(memory_reducer, true, "use memory reducer")
 DEFINE_BOOL(scavenge_reclaim_unmodified_objects, true,
             "remove unmodified and unreferenced objects")
 DEFINE_INT(heap_growing_percent, 0,
            "specifies heap growing factor as (1 + heap_growing_percent/100)")
 
 // execution.cc, messages.cc
-DEFINE_BOOL(clear_exceptions_on_js_entry, true,
+DEFINE_BOOL(clear_exceptions_on_js_entry, false,
             "clear pending exceptions when entering JavaScript")
 
 // counters.cc
 DEFINE_INT(histogram_interval, 600000,
            "time interval in ms for aggregating memory histograms")
 
 // global-handles.cc
 DEFINE_BOOL(trace_object_groups, false,
             "print object groups detected during each garbage collection")
 
@@ skipping 427 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA