The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/335cbdf575424fa4c2ae627f8b2221df670f4a52

commit 335cbdf575424fa4c2ae627f8b2221df670f4a52
Author: lizeb <lizeb@chromium.org>
Date: Fri Jun 02 10:49:00 2017

customtabs: Don't always destroy the spare WebContents before prerender.

No longer destroy the spare WebContents in the following cases:
- Prerender is requested but doesn't start. This is the case for 99% of
  stable users as of M58. In this case, don't penalize users.
- Forced prerenders. They are often discarded, and take a small amount
  of memory. In this case, the spare renderer is highly likely to be
  used later.

BUG= 728540 

Review-Url: https://codereview.chromium.org/2919433005
Cr-Commit-Position: refs/heads/master@{#476615}

[modify] https://crrev.com/335cbdf575424fa4c2ae627f8b2221df670f4a52/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
[modify] https://crrev.com/335cbdf575424fa4c2ae627f8b2221df670f4a52/chrome/android/javatests/src/org/chromium/chrome/browser/customtabs/CustomTabsConnectionTest.java