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This CL converts PrintHostMsg_GetDefaultPrintSettings message to
GetDefaultPrintSettings() in mojom::PrintManagerHost.

It introduces several helper functions to access PrinterQuery which
runs on IO thread. GetDefaultPrintSettings is called on UI thread
and posted to IO thread for PrintViewManagerBase to get the
settings.

It also updates PrintRenderFrameHelperTestBase with implementing
GetDefaultPrintSettings in TestPrintManagerHost and managing it
based on the frame.

Bug: 1008939
Change-Id: I873a7a4a3b3e46ca39880946724bcf8b3a2818b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2409467Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Julie Kim <jkim@igalia.com>
Cr-Commit-Position: refs/heads/master@{#809619}