Make Analyzer, VM and dart2js accept URI strings as part-of library identifier.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
diff --git a/runtime/vm/parser.cc b/runtime/vm/parser.cc
index 923526885ecea9685b32b527aa03bcd12b6b9592..2bde07453445bf8c21364fccde3fb073bfc70302 100644
--- a/runtime/vm/parser.cc
+++ b/runtime/vm/parser.cc
@@ -6194,12 +6194,16 @@ void Parser::ParsePartHeader() {
     ReportError("'part of' expected");
   }
   ConsumeToken();
-  // The VM is not required to check that the library name matches the
-  // name of the current library, so we ignore it.
-  ExpectIdentifier("library name expected");
-  while (CurrentToken() == Token::kPERIOD) {
-    ConsumeToken();
-    ExpectIdentifier("malformed library name");
+  // The VM is not required to check that the library name or URI matches the
+  // name or URI of the current library, so we ignore them.
+  if (CurrentToken() == Token::kSTRING) {
+    ParseStringLiteral(false);
+  } else {
+    ExpectIdentifier("library name expected");
+    while (CurrentToken() == Token::kPERIOD) {
+      ConsumeToken();
+      ExpectIdentifier("malformed library name");
+    }
   }
   ExpectSemicolon();
 }