android_webview: stop using system expat.

android_webview: stop using system expat.

To support unbundled updates we need to stop depending on system
libraries. Disable using the system version of libexpat and instead link
Chromium's copy, and stop removing the expat sources from the checkout.

This increases binary size by ~64KB.

Also remove an obsolete comment about using the system version of
sqlite; this was never implemented and now will not be.

BUG=409851
Committed: https://crrev.com/eac62b75ce57c1689a48fadd4229c1346509a170
Cr-Commit-Position: refs/heads/master@{#293115}

[Torne, 2014-09-02 14:46:46]

torne@chromium.org changed reviewers:
+ benm@chromium.org

[benm (inactive), 2014-09-02 17:57:57]

lgtm

[Torne, 2014-09-03 09:08:58]

The CQ bit was checked by torne@chromium.org

[commit-bot: I haz the power, 2014-09-03 09:09:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/torne@chromium.org/534603002/1

[commit-bot: I haz the power, 2014-09-03 09:57:55]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_clang_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)

[commit-bot: I haz the power, 2014-09-03 10:56:55]

Committed patchset #1 (id:1) as 5e200fa00f59d0e40e20151168f8a51a16a0cce2

[commit-bot: I haz the power, 2014-09-10 03:25:00]

Patchset 1 (id:??) landed as
https://crrev.com/eac62b75ce57c1689a48fadd4229c1346509a170
Cr-Commit-Position: refs/heads/master@{#293115}