Allow Observatory debugger to switch isolates.

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 388c0d327d330ee0b6800acc81ee737cf5eae971..44992eb02b714b7075263dff18800b293d63a34b 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -280,6 +280,9 @@ void JSONStream::PrintProperty(const char* name, intptr_t i) {
 
 
 void JSONStream::PrintProperty64(const char* name, int64_t i) {
+  // dart2js represents integers as double precision floats, which can
+  // represent anything in the range -2^53 ... 2^53.
+  ASSERT((-0x20000000000000LL <= i) && (i <= 0x20000000000000LL));

[Cutch, 2015/03/18 20:05:48]

How about:
#define MAX_JAVASCRIPT_INT 0x20000000000000LL
#define MIN_JAVASCRIPT_INT -MAX_JAVASCRIPT_INT

[turnidge, 2015/03/26 17:46:58]

Added IsJavascriptInt to utils.h.

   PrintPropertyName(name);
   PrintValue64(i);
 }