Added behind link_core_modules_separately flag to gyp files.

Added behind link_core_modules_separately flag to gyp files.

Also did the followings:
- added webcore_shared build target to core.gyp,
- moved some sources from core.gyp to core.gypi. So core.gyp uses variables defined in core.gypi.
- updated modules.gyp to see the flag,
- updated web.gyp to see the flag,


BUG=358074

[tasak, 2015-02-10 10:30:16]

tasak@google.com changed reviewers:
+ haraken@chromium.org

[tasak, 2015-02-10 10:30:16]

Would you review this CL?

[haraken, 2015-02-10 11:06:33]

LGTM

[tasak, 2015-02-10 11:20:00]

New patchsets have been uploaded after l-g-t-m from haraken@chromium.org

[tasak, 2015-02-10 12:39:59]

The CQ bit was checked by tasak@google.com

[commit-bot: I haz the power, 2015-02-10 12:40:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/907303002/20001

[commit-bot: I haz the power, 2015-02-10 12:43:53]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=189893

[caseq, 2015-02-10 13:20:28]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/907353002/ by caseq@chromium.org.

The reason for reverting is: Reverting as the primary suspect of android build
failure:
http://build.chromium.org/p/chromium.webkit/builders/Android%20Builder%20%28d....