Implement Blob.close().

LayoutTests/fast/files/blob-close-read-expected.txt

Index: LayoutTests/fast/files/blob-close-read-expected.txt
diff --git a/LayoutTests/fast/files/blob-close-read-expected.txt b/LayoutTests/fast/files/blob-close-read-expected.txt
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+Test the Blob.close() method, reading.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+Testing that the reading of closed Blobs fail.
+PASS blob.close(); blob.size is 0
+PASS reader.readAsArrayBuffer(blob) threw exception InvalidStateError: Failed to execute 'readAsArrayBuffer' on 'FileReader': Blob has been closed..
+PASS reader.readAsBinaryString(blob) threw exception InvalidStateError: Failed to execute 'readAsBinaryString' on 'FileReader': Blob has been closed..
+PASS reader.readAsText(blob) threw exception InvalidStateError: Failed to execute 'readAsText' on 'FileReader': Blob has been closed..
+PASS reader.readAsDataURL(blob) threw exception InvalidStateError: Failed to execute 'readAsDataURL' on 'FileReader': Blob has been closed..
+Testing that ongoing async reads aren't interrupted by close()
+PASS reader2.readAsArrayBuffer(blob) threw exception InvalidStateError: Failed to execute 'readAsArrayBuffer' on 'FileReader': Blob has been closed..
+PASS blob.size is 0
+PASS FileReader loaded: 0123456789abcdef
+PASS readAsText() completed
+PASS blob.size is 0
+Testing that sliced reads aren't affected by close() on 'parent' Blob.
+PASS sliced.size is 14
+PASS result is "23456789abcdef"
+PASS readAsText() completed
+PASS sliced.size is 14
+PASS successfullyParsed is true
+
+TEST COMPLETE
+