[foozzie] Suppress crbug.com/688159

BUG=chromium:688159
NOTRY=true
TBR=bmeurer@chromium.org,mstarzinger@chromium.org

Change-Id: I9b5c0c531af31534a0dd33e078a148b822834448
Reviewed-on: https://chromium-review.googlesource.com/439184Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43053}

tools/foozzie/v8_suppressions.py

@@ -45,7 +45,6 @@ IGNORE_SOURCES = {
     '/v8/test/mjsunit/regress/regress-2989.js',
   ],
 
-  # crbug.com/681088
   'crbug.com/681088': [
     '/v8/test/mjsunit/asm/asm-validation.js',
     '/v8/test/mjsunit/asm/b5528-comma.js',
@@ -60,11 +59,14 @@ IGNORE_SOURCES = {
     '/v8/test/mjsunit/wasm/asm-wasm-stack.js',
   ],
 
-  # crbug.com/681241
   'crbug.com/681241': [
     '/v8/test/mjsunit/regress/regress-617526.js',
     '/v8/test/mjsunit/regress/wasm/regression-02862.js',
   ],
+
+  'crbug.com/688159': [
+    '/v8/test/mjsunit/es7/exponentiation-operator.js',
+  ],
 }
 
 # Ignore by test case pattern. Map from bug->regexp.