Model each Dart library as its own ScriptState when devtools are enabled.

LayoutTests/dart/inspector/evaluate-in-console-expected.txt

Index: LayoutTests/dart/inspector/evaluate-in-console-expected.txt
diff --git a/LayoutTests/dart/inspector/evaluate-in-console-expected.txt b/LayoutTests/dart/inspector/evaluate-in-console-expected.txt
index e78536ab2ecd58ebd47b05af6e19822091fd83ff..aaa4c25654921f3c0c867751e85df42197d17598 100644
--- a/LayoutTests/dart/inspector/evaluate-in-console-expected.txt
+++ b/LayoutTests/dart/inspector/evaluate-in-console-expected.txt
@@ -45,11 +45,11 @@ new Element.tag("div").outerHtml = "<div></div>"
 new Element.tag("div").tagName = "DIV"
 intList.toString() = "{4, 2}"
 (LinkedList).toString() = "LinkedList"
-$var.a=new List<int>()..add(4)..add(42) = 
-$var.a.toString() = "[4, 42]"
-$var.variables() = 
-$var.f = (x) => x*42 = [Dart Function] {}
-$var.f(2) = 84
+var a=new List<int>()..add(4)..add(42) = 
+a.toString() = "[4, 42]"
+$consoleVariables.variables() = 
+var f = (x) => x*42 = [Dart Function] {}
+f(2) = 84
 [] is List = true
 {} is List = false
 "This should be an int: ${10000000000000000000000 - 1}" = "This should be an int: 9999999999999999999999"