The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eb8ba65e8150c82259ec8c07b37db279011a06b8

commit eb8ba65e8150c82259ec8c07b37db279011a06b8
Author: Felix <zpeng@chromium.org>
Date: Fri Aug 18 15:55:13 2017

Clean up unnecessary extra pak files for WebView apps.

This CL cleans up unnecessary extra pak files for WebView apps by
removing "paks" directory from "app_webview" directory if it exists.

We have following Chrome versions for testings: (as 2017/08/17)
Stable (60, extracting extra pak files)
Dev (61, extracting extra pak files)
Canary (62, no longer extracting extra pak files, no clean up)
Debug (62, no longer extracting extra pak files, with clean up)

Tested with Gmail and WebView shell browser:
Test 1:
Open app with Stable -> extra paks generated
Switch to Debug -> extra paks removed
Test 2:
Open app with Stable -> extra paks generated
Switch to Dev -> extra paks persist
Test 3:
Open app with Stable -> extra paks generated
Switch to Canary -> extra paks persist

Bug:  755675 
Change-Id: I220d1c8857b16a14566458c4bf9f1c37f3ee5655
Reviewed-on: https://chromium-review.googlesource.com/619179
Commit-Queue: Felix <zpeng@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495556}
[modify] https://crrev.com/eb8ba65e8150c82259ec8c07b37db279011a06b8/android_webview/java/src/org/chromium/android_webview/AwBrowserProcess.java