Make Blob constructor's first argument optional.

third_party/WebKit/LayoutTests/fast/files/blob-constructor.html

Index: third_party/WebKit/LayoutTests/fast/files/blob-constructor.html
diff --git a/third_party/WebKit/LayoutTests/fast/files/blob-constructor.html b/third_party/WebKit/LayoutTests/fast/files/blob-constructor.html
index cdf4684e0fc111eeb9507a10f73dc7ae6a5cd117..c46cd1584516148585fafdaaf07dd8561ebcb52c 100644
--- a/third_party/WebKit/LayoutTests/fast/files/blob-constructor.html
+++ b/third_party/WebKit/LayoutTests/fast/files/blob-constructor.html
@@ -7,6 +7,7 @@ var jsTestIsAsync = true;
 
 // Test the different ways you can construct a Blob.
 shouldBeTrue("(new Blob()) instanceof window.Blob");
+shouldBeTrue("(new Blob(undefined)) instanceof window.Blob");
 shouldBeTrue("(new Blob([])) instanceof window.Blob");
 shouldBeTrue("(new Blob(['hello'])) instanceof window.Blob");
 shouldBeTrue("(new Blob(['hello'], {})) instanceof window.Blob");
@@ -14,6 +15,12 @@ shouldBeTrue("(new Blob(['hello'], {type:'text/html'})) instanceof window.Blob")
 shouldBeTrue("(new Blob(['hello'], {type:'text/html', endings:'native'})) instanceof window.Blob");
 shouldBeTrue("(new Blob(['hello'], {type:'text/html', endings:'transparent'})) instanceof window.Blob");
 
+// Test default sizes/types.
+shouldBe("(new Blob()).size", "0");
+shouldBe("(new Blob(undefined)).size", "0");
+shouldBeEqualToString("(new Blob()).type", "");
+shouldBeEqualToString("(new Blob(undefined)).type", "");
+
 // Test invalid blob parts.
 shouldThrow("new Blob('hello')", '"TypeError: Failed to construct \'Blob\': The 1st argument is neither an array, nor does it have indexed properties."');
 shouldThrow("new Blob(0)", '"TypeError: Failed to construct \'Blob\': The 1st argument is neither an array, nor does it have indexed properties."');