Example test results:
https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Linux_Trusty_Leak/4841/layout-test-results/results.html

Test:
external/wpt/html/semantics/scripting-1/the-script-element/module/import-subgraph-404.html

Leak log:
({"numberOfLiveDocuments":[1,2],"numberOfLiveNodes":[4,21],"numberOfLiveResources":[0,2],"numberOfLiveSuspendableObjects":[2,3]})

This looks like it's most likely related to  bug 718114 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8957c48873b71b2bf23a17b5e43d7cd625a0ebb5

commit 8957c48873b71b2bf23a17b5e43d7cd625a0ebb5
Author: qyearsley <qyearsley@chromium.org>
Date: Sat May 20 21:13:51 2017

Add leak expectation for external/wpt/.../module/import-subgraph-404.html.

TBR=hiroshige
TBR_REASON=Sheriffing/gardening leak builder
BUG= 724818 

Review-Url: https://codereview.chromium.org/2895053002
Cr-Commit-Position: refs/heads/master@{#473449}

[modify] https://crrev.com/8957c48873b71b2bf23a17b5e43d7cd625a0ebb5/third_party/WebKit/LayoutTests/LeakExpectations

Removing from the sheriff-queue, since this seems to be assigned and being worked on already.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5

commit 74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5
Author: Kouhei Ueno <kouhei@chromium.org>
Date: Mon May 29 13:08:43 2017

[ES6 modules] Detach ScriptModuleResolverImpl refs when detaching context.

Before this CL, we kept around strong v8::Module refs from
ScriptModuleResolverImpl after the context is detached.
v8::Module refers to the settings object Document via Modulator, so
lead to leaks detected by Blink Leak Detector.

This CL detaches the v8::Module strong refs from ScriptModuleResolverImpl
when we detach Document from the context.

This CL is meant to be a temporary fix. Ideally, we should convert
all v8::Module refs in ScriptModuleResolverImpl to weak refs.
However, it is not trivial as we need to rework ScriptModule.

Bug:  594639 , 725816,  724818 
Change-Id: If5b697bc87b9cd907333be0afe713888c1be2cf9
Reviewed-on: https://chromium-review.googlesource.com/517525
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#475340}
[modify] https://crrev.com/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5/third_party/WebKit/LayoutTests/LeakExpectations
[modify] https://crrev.com/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5/third_party/WebKit/Source/core/dom/ModulatorImpl.cpp
[modify] https://crrev.com/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5/third_party/WebKit/Source/core/dom/ScriptModuleResolverImpl.cpp
[modify] https://crrev.com/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5/third_party/WebKit/Source/core/dom/ScriptModuleResolverImpl.h
[modify] https://crrev.com/74ba772e23ab732e4d4f2c2c2bcd76fbff9c78d5/third_party/WebKit/Source/core/dom/ScriptModuleResolverImplTest.cpp