This reverts commit 3b3248da.

Reason for revert: 
Test crashing on all bots.
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8931832645289538640/+/steps/blink_platform_unittests/0/logs/BitmapImageTest.DecoderAndCacheMipLevels/0
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=blink_platform_unittests&tests=BitmapImageTest.DecoderAndCacheMipLevels
https://bugs.chromium.org/p/chromium/issues/attachment?aid=364338&signed_aid=j6fGrtk-5lTyU5qtiDtjbg==&inline=1

Original change's description:
> Move image resources for bitmap_image_test to /testing/data
> 
> This pacth means blink/renderer/platform/graphics/bitmap_image_test.cc
> loads images from blink/renderer/platform/testing/data.
> This will more cleanly separate the unit test and layout test data.
> 
> Bug: 898155
> Change-Id: I34f582f127df6fff8634aaff66893fb27abffaaa
> Reviewed-on: https://chromium-review.googlesource.com/c/1296870
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Commit-Queue: Jaeyong Bae <jdragon.bae@gmail.com>
> Cr-Commit-Position: refs/heads/master@{#602168}

TBR=pdr@chromium.org,jdragon.bae@gmail.com

Change-Id: I2996bdfa2fdf7bcba544b8925bc33da5b634a8df
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 898155
Reviewed-on: https://chromium-review.googlesource.com/c/1296938Reviewed-by: Alan Cutter <alancutter@chromium.org>
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602221}