DOMException toString is not correct

LayoutTests/http/tests/security/canvas-remote-read-remote-image-expected.txt

 CONSOLE MESSAGE: Unable to get image data from canvas because the canvas has been tainted by cross-origin data.
 CONSOLE MESSAGE: Unable to get image data from canvas because the canvas has been tainted by cross-origin data.
 CONSOLE MESSAGE: Unable to get image data from canvas because the canvas has been tainted by cross-origin data.
 CONSOLE MESSAGE: Unable to get image data from canvas because the canvas has been tainted by cross-origin data.
 Untainted canvas:
 PASS: Calling getImageData() from an untainted canvas was allowed.
 PASS: Calling toDataURL() on an untainted canvas was allowed.
 
 
 Tainted canvas:
-PASS: Calling getImageData() from a canvas tainted by a remote image was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling toDataURL() on a canvas tainted by a remote image was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling getImageData() from a canvas tainted by a tainted canvas was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling toDataURL() on a canvas tainted by a tainted canvas was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling getImageData() from a canvas tainted by a remote image tainted pattern was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling toDataURL() on a canvas tainted by a remote image tainted pattern was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling getImageData() from a canvas tainted by a tainted canvas pattern was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
-PASS: Calling toDataURL() on a canvas tainted by a tainted canvas pattern was not allowed - Threw error: Error: SecurityError: DOM Exception 18.
+PASS: Calling getImageData() from a canvas tainted by a remote image was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling toDataURL() on a canvas tainted by a remote image was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling getImageData() from a canvas tainted by a tainted canvas was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling toDataURL() on a canvas tainted by a tainted canvas was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling getImageData() from a canvas tainted by a remote image tainted pattern was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling toDataURL() on a canvas tainted by a remote image tainted pattern was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling getImageData() from a canvas tainted by a tainted canvas pattern was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..
+PASS: Calling toDataURL() on a canvas tainted by a tainted canvas pattern was not allowed - Threw error: SecurityError: An attempt was made to break through the security policy of the user agent..