[android_webview] Extract common SystemWebview parameters to .gypi file.

[android_webview] Extract common SystemWebview parameters to .gypi file.

This extracts the common SystemWebview gyp params to a shared .gypi file.

BUG=None
TEST=compiles

Committed: https://crrev.com/c5bdcca1573b6dd37eb828877fff8d136f8c7e7b
Cr-Commit-Position: refs/heads/master@{#301100}

[mkosiba (inactive), 2014-10-24 10:27:47]

Patchset #2 (id:20001) has been deleted

[mkosiba (inactive), 2014-10-24 10:28:52]

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

[Torne, 2014-10-24 12:39:52]

lgtm

[mkosiba (inactive), 2014-10-24 13:53:09]

The CQ bit was checked by mkosiba@chromium.org

[commit-bot: I haz the power, 2014-10-24 13:54:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/677033002/60001

[commit-bot: I haz the power, 2014-10-24 14:36:44]

Committed patchset #3 (id:60001)

[commit-bot: I haz the power, 2014-10-24 14:37:44]

Patchset 3 (id:??) landed as
https://crrev.com/c5bdcca1573b6dd37eb828877fff8d136f8c7e7b
Cr-Commit-Position: refs/heads/master@{#301100}