[mjsunit] Fix error message for assertEqualsDelta

Before:
Failure: expected <true> found <false>

After:
Failure: expected <0.4 +- 0.001> found <0.3>

R=ahaas@chromium.org

Change-Id: I304fd90112cb7131103863813e7b0920be2b5c04
Reviewed-on: https://chromium-review.googlesource.com/456284Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43950}

test/mjsunit/mjsunit.js

@@ -333,7 +333,9 @@ var failWithMessage;
 
   assertEqualsDelta =
       function assertEqualsDelta(expected, found, delta, name_opt) {
-    assertTrue(Math.abs(expected - found) <= delta, name_opt);
+    if (Math.abs(expected - found) > delta) {
+      fail(PrettyPrint(expected) + " +- " + PrettyPrint(delta), found, name_opt);
+    }
   };