Don't forward invalid line offsets for generated scripts to Dart_Load*.

Source/bindings/dart/DartAsyncLoader.cpp

Index: Source/bindings/dart/DartAsyncLoader.cpp
diff --git a/Source/bindings/dart/DartAsyncLoader.cpp b/Source/bindings/dart/DartAsyncLoader.cpp
index 7f64cd70e494d83f3edff3407fb280c3c2adae27..becb391fc9eba35e7e68caf90b97e9a7e5a27d1f 100644
--- a/Source/bindings/dart/DartAsyncLoader.cpp
+++ b/Source/bindings/dart/DartAsyncLoader.cpp
@@ -203,7 +203,11 @@ void DartAsyncLoader::processRequests(Dart_Isolate isolate, const String& script
             // Inline script.
             ASSERT(!m_pendingLibraries.contains(url));
             m_pendingLibraries.add(url);
-            process(script->url(), script->scriptContent(), script->startLineNumber().zeroBasedInt());
+            intptr_t lineOffset = script->startLineNumber().zeroBasedInt();
+            // Blink gives generated script tags an invalid start line.
+            if (lineOffset < 0)
+                lineOffset = 0;
+            process(script->url(), script->scriptContent(), lineOffset);
         } else {
             // Canonicalize the src attribute url.
             String canonical = KURL(script->ownerDocument()->url(), src).string();