Detect <link rel='manifest'> and notify embedder.

Source/core/testing/Internals.cpp

Index: Source/core/testing/Internals.cpp
diff --git a/Source/core/testing/Internals.cpp b/Source/core/testing/Internals.cpp
index 10f83a5affbba066e4aed8d8cd1ffabc9002db29..e53e09f191be75e864ca22e721d0c825d70f34c4 100644
--- a/Source/core/testing/Internals.cpp
+++ b/Source/core/testing/Internals.cpp
@@ -2369,4 +2369,14 @@ String Internals::textSurroundingNode(Node* node, int x, int y, unsigned long ma
     return surroundingText.content();
 }
 
+String Internals::manifestURL(Document* document, ExceptionState& exceptionState)
+{
+    if (!document) {
+        exceptionState.throwDOMException(InvalidAccessError, "No context document is available.");
+        return String();
+    }
+
+    return document->manifestURL().string();
+}
+
 }