Don't double-escape in strings in the VM Service, and don't use \u0000 to determine the string lengt

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 762124d1c26f04caebca29650c765a6645192107..b77b01f3d4e67a57bdb32bfb34a18cc07167750e 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -217,6 +217,14 @@ void JSONStream::PrintValue(const char* s) {
 }
 
 
+void JSONStream::PrintValue(const char* s, intptr_t len) {
+  PrintCommaIfNeeded();
+  buffer_.AddChar('"');
+  AddEscapedUTF8String(s, len);
+  buffer_.AddChar('"');
+}
+
+
 void JSONStream::PrintValueNoEscape(const char* s) {
   PrintCommaIfNeeded();
   buffer_.Printf("%s", s);
@@ -302,6 +310,12 @@ void JSONStream::PrintProperty(const char* name, const char* s) {
 }
 
 
+void JSONStream::PrintProperty(const char* name, const char* s, intptr_t len) {
+  PrintPropertyName(name);
+  PrintValue(s, len);
+}
+
+
 void JSONStream::PrintPropertyNoEscape(const char* name, const char* s) {
   PrintPropertyName(name);
   PrintValueNoEscape(s);
@@ -412,6 +426,14 @@ void JSONStream::AddEscapedUTF8String(const char* s) {
     return;
   }
   intptr_t len = strlen(s);
+  AddEscapedUTF8String(s, len);
+}
+
+
+void JSONStream::AddEscapedUTF8String(const char* s, intptr_t len) {
+  if (s == NULL) {
+    return;
+  }
   const uint8_t* s8 = reinterpret_cast<const uint8_t*>(s);
   intptr_t i = 0;
   for (; i < len; ) {