[test] Shorten excessive webkit test.

BUG=

Review URL: https://codereview.chromium.org/1257583005

Cr-Commit-Position: refs/heads/master@{#29895}

test/webkit/fast/js/excessive-comma-usage-expected.txt

@@ -28,7 +28,7 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 
 PASS new Function(initializerTestString)() is true
 PASS new Function(declarationTestString)() is true
-FAIL new Function(commaExpressionTestString)() should be true. Threw exception RangeError: Maximum call stack size exceeded
+PASS new Function(commaExpressionTestString)() is true
 PASS successfullyParsed is true
 
 TEST COMPLETE

test/webkit/fast/js/excessive-comma-usage.js

@@ -24,17 +24,17 @@
 description("Test that we can handle excessively large initializer lists");
 
 var initializerTestString = "var a=0";
-for (var i = 0; i < 50000; i++)
+for (var i = 0; i < 5000; i++)
     initializerTestString += ",a"+i+"="+i;
 initializerTestString += ";return true;";
 
 var declarationTestString = "var a";
-for (var i = 0; i < 50000; i++)
+for (var i = 0; i < 5000; i++)
     declarationTestString += ",a"+i;
 declarationTestString += ";return true;";
 
 var commaExpressionTestString = "1";
-for (var i = 0; i < 50000; i++)
+for (var i = 0; i < 5000; i++)
     commaExpressionTestString += ",1";
 commaExpressionTestString += ";return true;";