mark devtools/coverage/multiple-instances-merge.js timeout at Win7 bot

Tbr: caseq@chromium.org
Bug: 848799
Change-Id: Ifda052f25cfb33847a79b590c38e85b072c9cfc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1543810
Commit-Queue: Ella Ge <eirage@chromium.org>
Reviewed-by: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645393}

third_party/blink/web_tests/TestExpectations

@@ -6132,6 +6132,8 @@ crbug.com/946712 [ Release ] http/tests/devtools/elements/styles-2/paste-propert
 crbug.com/946712 [ Release ] virtual/binary-for-devtools/http/tests/devtools/elements/styles-2/paste-property.js [ Crash Pass Timeout ]
 crbug.com/946713 [ Release ] http/tests/devtools/extensions/extensions-resources.js [ Crash Pass Timeout ]
 crbug.com/946713 [ Release ] virtual/binary-for-devtools/http/tests/devtools/extensions/extensions-resources.js [ Crash Pass Timeout ]
+crbug.com/848799 [ Win7 ] http/tests/devtools/coverage/multiple-instances-merge.js [ Pass Timeout ]
+crbug.com/848799 [ Win7 ] virtual/binary-for-devtools/http/tests/devtools/coverage/multiple-instances-merge.js [ Pass Timeout ]
 
 ### external/wpt/fetch/sec-metadata/
 crbug.com/947023 external/wpt/fetch/sec-metadata/embed.tentative.https.sub.html [ Pass Failure ]