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

Review URL: https://codereview.chromium.org/916003002

Cr-Commit-Position: refs/heads/master@{#316422}
1 file changed