site-per-process: Mark iframe-script-modify-attr.htm as crashing again

The test is still crashing on linux_chromium_rel_ng and blocking WPT
imports:
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45486
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45507
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45582
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45602
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45638
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45651
* https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux_chromium_rel_ng/45722

TBR=lukasza,leon.han@intel.com

Bug: 801992
Change-Id: Ie51d1c04d9ed23ff7aeea1a4f3e485ab97acd3bc
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/962146Reviewed-by: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#543058}

third_party/WebKit/LayoutTests/FlagExpectations/site-per-process

@@ -143,6 +143,7 @@ crbug.com/801992 external/wpt/content-security-policy/frame-ancestors/frame-ance
 crbug.com/801992 external/wpt/content-security-policy/frame-ancestors/frame-ancestors-nested-same-in-cross-url-allow.html [ Pass Timeout ]
 crbug.com/801992 external/wpt/content-security-policy/frame-ancestors/frame-ancestors-star-allow-crossorigin.html [ Pass Timeout ]
 crbug.com/801992 external/wpt/html/browsers/the-window-object/security-window/window-security.html [ Pass Timeout ]
+crbug.com/801992 http/tests/misc/iframe-script-modify-attr.html [ Pass Crash ]
 
 crbug.com/711468 virtual/gpu/fast/canvas/canvas-composite-image.html [ Pass Timeout ]
 crbug.com/711468 virtual/gpu/fast/canvas/canvas-scale-strokePath-shadow.html [ Pass Timeout ]