Add support for interrupting an isolate in the vm. Interrupts are

runtime/vm/assert.h

Index: runtime/vm/assert.h
===================================================================
--- runtime/vm/assert.h	(revision 2528)
+++ runtime/vm/assert.h	(working copy)
@@ -49,6 +49,9 @@
   void StringEquals(const E& expected, const A& actual);
 
   template<typename E, typename A>
+  void IsSubstring(const E& needle, const A& haystack);
+
+  template<typename E, typename A>
   void LessThan(const E& left, const A& right);
 
   template<typename E, typename A>
@@ -140,6 +143,18 @@
 
 
 template<typename E, typename A>
+void DynamicAssertionHelper::IsSubstring(const E& needle, const A& haystack) {
+  std::stringstream ess, ass;
+  ess << needle;
+  ass << haystack;
+  std::string es = ess.str(), as = ass.str();
+  if (as.find(es) != std::string::npos) return;
+  Fail("expected <\"%s\"> to be a substring of <\"%s\">",
+       es.c_str(), as.c_str());
+}
+
+
+template<typename E, typename A>
 void DynamicAssertionHelper::LessThan(const E& left, const A& right) {
   if (left < right) return;
   std::stringstream ess, ass;
@@ -248,6 +263,9 @@
 #define EXPECT_STREQ(expected, actual)                                         \
   dart::Expect(__FILE__, __LINE__).StringEquals((expected), (actual))
 
+#define EXPECT_SUBSTRING(needle, haystack)                                     \
+  dart::Expect(__FILE__, __LINE__).IsSubstring((needle), (haystack))
+
 #define EXPECT_LT(left, right)                                                 \
   dart::Expect(__FILE__, __LINE__).LessThan((left), (right))