Making the ChildProcessServiceImpl constructor public seems to fix things.

One interesting property of this bug that I don't yet understand is that after creating the renderer for the WebAPK fails, creating subsequent renderers for normal tabs also fails. I did some investigation. It seems like we are looping forever in while (sSpareConnectionStarting) in ChildProcessLauncher#startInternal()

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/feb7ca146e6cd6662129d0b82dfe116b94d37ad1

commit feb7ca146e6cd6662129d0b82dfe116b94d37ad1
Author: pkotwicz <pkotwicz@chromium.org>
Date: Tue Feb 14 02:37:20 2017

Fix WebAPK renderer not launching

WebApkSandboxedService creates ChildProcessServiceImpl via reflection.
https://codereview.chromium.org/2675013002 added a non public constructor to
ChildProcessServiceImpl causing construction-via-reflection to fail.

BUG= 691709 , 691724 

Review-Url: https://codereview.chromium.org/2692023003
Cr-Commit-Position: refs/heads/master@{#450207}

[modify] https://crrev.com/feb7ca146e6cd6662129d0b82dfe116b94d37ad1/content/public/android/java/src/org/chromium/content/app/ChildProcessServiceImpl.java