Add untrusted NaCl build for PPAPI proxy.

Add untrusted NaCl build for PPAPI proxy.
This patch refactors ppapi_shared.gypi and ppapi_proxy.gypi into proper includes, adds ppapi_shared_untrusted and ppapi_proxy_untrusted .gyp files, and integrates them into the nacl_irt build (ppapi/native_client/native_client.gyp). In order to build without link errors, it includes our plugin side initialization of PluginDispatcher, and a PpapiPluginMain definition. When the 'build_ppapi_ipc_proxy_untrusted' gyp flag is set to '1', this will build a working NaCl IRT using the Chrome IPC proxy.
BUG=116317
TEST=compiles, runs HelloWorld and GetURL SDK examples.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=142540

[bbudge, 2012-06-15 22:57:42]

I had to revert the previous CL because it broke when disable_nacl==0. Changes
only all.gyp

[brettw, 2012-06-15 22:59:10]

lgtm

[bbudge, 2012-06-15 23:05:39]

+bradn for his take. This was necessary to keep disable_nacl==1 folks building.

[commit-bot: I haz the power, 2012-06-15 23:08:55]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/bbudge@chromium.org/10565015/1

[commit-bot: I haz the power, 2012-06-16 00:35:02]

Change committed as 142540