Mark external/wpt/IndexedDB/keypath-exceptions.htm as flaky

...on all platforms.

TBR: jsbell@chromium.org
Bug: 1045260
Change-Id: Ibd76abb328bb2737675dd0c6768407f1fb5bd8c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2017332Reviewed-by: Martin Šrámek <msramek@chromium.org>
Commit-Queue: Martin Šrámek <msramek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734865}

third_party/blink/web_tests/TestExpectations

@@ -6503,3 +6503,5 @@ crbug.com/1045050 [ Mac ] virtual/gpu-rasterization/images/sprite-no-bleed.html
 crbug.com/1045050 [ Linux ] virtual/prefer_compositing_to_lcd_text/compositing/overflow/mask-with-filter.html [ Pass Failure ]
 crbug.com/1045050 [ Linux ] virtual/prefer_compositing_to_lcd_text/compositing/overflow/nested-render-surfaces-with-rotation.html [ Pass Failure ]
 crbug.com/1045050 [ Linux ] virtual/prefer_compositing_to_lcd_text/compositing/overflow/rotate-then-clip-effect-interleave.html [ Pass Failure ]
+
+crbug.com/1045260 external/wpt/IndexedDB/keypath-exceptions.htm [ Pass Failure ]