Fix a crash for ppb_pdf_impl.cc under single process model

Fix a crash for ppb_pdf_impl.cc under single process model

In PPB_PDF_Impl::SetPrintClient where CHECK(!g_print_client) may fail under
--single-process model, since code here is to expect there to be only one
g_print_client instance within a render process(thread). But --single-process
model will create all RenderThread in a single process, thus g_print_client may
be created many times in a single process and CHECK(!g_print_client) will fail.

In this patch we will change g_print_client from process-level to
RenderThread-level, since every render process will only keep one RenderThread.

BUG=457580
Committed: https://crrev.com/1251f5f51de3d611c74535883f8263b3283eca69
Cr-Commit-Position: refs/heads/master@{#316422}

[jinlong.zhai, 2015-02-11 09:40:04]

jinlong.zhai@samsung.com changed reviewers:
+ dmichael@chromium.org

[jinlong.zhai, 2015-02-11 09:40:04]

Please help to look at this patch.

Thanks,
Jinlong

[dmichael (off chromium), 2015-02-11 17:35:00]

lgtm

https://codereview.chromium.org/916003002/diff/1/components/pdf/renderer/ppb_...
File components/pdf/renderer/ppb_pdf_impl.cc (right):

https://codereview.chromium.org/916003002/diff/1/components/pdf/renderer/ppb_...
components/pdf/renderer/ppb_pdf_impl.cc:41: g_print_client_tls =
LAZY_INSTANCE_INITIALIZER;
Please add a comment briefly explaining why we're using TLS here, and reference
the bug.

[jinlong.zhai, 2015-02-15 07:38:01]

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

[jinlong.zhai, 2015-02-15 07:40:47]

hi, dmichael
  I have added a comment and reference the bug.
  Please take a look at it again.

thanks,
Jinlong

[jinlong.zhai, 2015-02-16 01:35:03]

The CQ bit was checked by jinlong.zhai@samsung.com

[commit-bot: I haz the power, 2015-02-16 01:35:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/916003002/40001

[commit-bot: I haz the power, 2015-02-16 02:28:36]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-02-16 02:29:10]

Patchset 3 (id:??) landed as
https://crrev.com/1251f5f51de3d611c74535883f8263b3283eca69
Cr-Commit-Position: refs/heads/master@{#316422}