Would be split to several steps:
1. build a OfflinePageEvaluationBridge
2. add Java test and tweak existing code for adapting
3. make a wrapper for easier use
maybe more

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3f2464af861c43de538fd23801b12931b93c004a

commit 3f2464af861c43de538fd23801b12931b93c004a
Author: romax <romax@chromium.org>
Date: Fri Oct 14 19:17:08 2016

[Offline Pages] Added OfflinePageEvaluationBridge for testing.

Build another bridge for evaluation tests use only. This is part of a larger
change tracked in the bug. The bridge exposes some testing only interface and
implements another observer.
The bridge would not be compiled for official build, and currently there seems
no way to have testing-only JNI code without marking with build flags.

BUG= 646947 

Review-Url: https://codereview.chromium.org/2378803003
Cr-Commit-Position: refs/heads/master@{#425419}

[add] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/evaluation/OfflinePageEvaluationBridge.java
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/android/java_sources.gni
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/browser/BUILD.gn
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/browser/android/chrome_jni_registrar.cc
[add] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/browser/android/offline_pages/evaluation/offline_page_evaluation_bridge.cc
[add] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/chrome/browser/android/offline_pages/evaluation/offline_page_evaluation_bridge.h
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/components/offline_pages/BUILD.gn
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/components/offline_pages/background/BUILD.gn
[modify] https://crrev.com/3f2464af861c43de538fd23801b12931b93c004a/components/offline_pages/background/request_notifier.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c1f5c1b9927576a524b1fe3476035f4d1128e79

commit 1c1f5c1b9927576a524b1fe3476035f4d1128e79
Author: romax <romax@chromium.org>
Date: Wed Oct 19 01:49:48 2016

[Offline Pages] Add evaluation test support in RequestCoodinator.

Added the function to add customized callback which would be called
after an user request is completed. Also fixed the issue where the
scheduler callback would not be invoked if there's a failure during the
offlining, also made it have the same behavior as described in comments.
Changed some tests regarding to the changes above.

BUG= 653708 , 646947 

Review-Url: https://chromiumcodereview.appspot.com/2425873003
Cr-Commit-Position: refs/heads/master@{#426115}

[modify] https://crrev.com/1c1f5c1b9927576a524b1fe3476035f4d1128e79/components/offline_pages/background/offliner_policy.h
[modify] https://crrev.com/1c1f5c1b9927576a524b1fe3476035f4d1128e79/components/offline_pages/background/request_coordinator.cc
[modify] https://crrev.com/1c1f5c1b9927576a524b1fe3476035f4d1128e79/components/offline_pages/background/request_coordinator.h
[modify] https://crrev.com/1c1f5c1b9927576a524b1fe3476035f4d1128e79/components/offline_pages/background/request_coordinator_unittest.cc
[modify] https://crrev.com/1c1f5c1b9927576a524b1fe3476035f4d1128e79/components/offline_pages/background/request_picker_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b

commit de5e277b78cc3e4ad3a061ae838ec8b9885ea38b
Author: romax <romax@chromium.org>
Date: Thu Oct 27 02:04:59 2016

[Offline Pages] Add basic evaluation tests and related changes.

This change includes some changes for the basic evaluation tests.
1. Evaluation Java test file.
2. Evaluation scheduler which would only be used in testing and will
start the processing of requests immediately. This will be injected in
request coordinator factory as a testing class.
3. Build files related.

BUG= 646947 

Review-Url: https://codereview.chromium.org/2432593002
Cr-Commit-Position: refs/heads/master@{#427913}

[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/evaluation/OfflinePageEvaluationBridge.java
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/android/java_sources.gni
[add] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/android/javatests/src/org/chromium/chrome/browser/offlinepages/OfflinePageSavePageLaterEvaluationTest.java
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/BUILD.gn
[add] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/evaluation/evaluation_test_scheduler.cc
[add] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/evaluation/evaluation_test_scheduler.h
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/evaluation/offline_page_evaluation_bridge.cc
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/evaluation/offline_page_evaluation_bridge.h
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/request_coordinator_factory.cc
[modify] https://crrev.com/de5e277b78cc3e4ad3a061ae838ec8b9885ea38b/chrome/browser/android/offline_pages/request_coordinator_factory.h

Next steps are tracking in 647008 - build a tool wrapping the test running and handling input/output etc.