Introduce a flag to force program abort on type/assertion errors.

runtime/lib/errors.cc

Index: runtime/lib/errors.cc
diff --git a/runtime/lib/errors.cc b/runtime/lib/errors.cc
index aa985da68c3127bd66d261e8d0542235f45cf91f..434143b30e3de86ec39258dcad8448464867184f 100644
--- a/runtime/lib/errors.cc
+++ b/runtime/lib/errors.cc
@@ -10,11 +10,17 @@
 
 namespace dart {
 
+DECLARE_FLAG(bool, abort_on_assertion_errors);
+
 // Allocate and throw a new AssertionError.
 // Arg0: index of the first token of the failed assertion.
 // Arg1: index of the first token after the failed assertion.
 // Return value: none, throws an exception.
 DEFINE_NATIVE_ENTRY(AssertionError_throwNew, 2) {
+  if (FLAG_abort_on_assertion_errors) {
+    Exceptions::PrintStackTraceAndAbort("an assertion failure");
+  }
+
   // No need to type check the arguments. This function can only be called
   // internally from the VM.
   intptr_t assertion_start =