[pdf] Call pp::PDF::Print() synchronously

Call pp::PDF::Print() synchronously in the Pepper viewer, instead of
posting a task to the main thread. The old implementation was an
artifact of the days when the PDF plugin was in-process and re-entrancy
was a risk. But now that the plugin is out-of-process, pp::PDF::Print()
already invokes the print dialog asynchronously across the process
boundary to the renderer.

Change-Id: Iabc0dcfc561492353cb666ad6569059e52d87ed6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2964274
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#894043}

pdf/out_of_process_instance.cc

@@ -1252,10 +1252,7 @@ void OutOfProcessInstance::OnPrintPreviewLoaded() {
 }
 
 void OutOfProcessInstance::InvokePrintDialog() {
-  ScheduleTaskOnMainThread(FROM_HERE,
-                           base::BindOnce(&OutOfProcessInstance::OnPrint,
-                                          weak_factory_.GetWeakPtr()),
-                           /*result=*/0, base::TimeDelta());
+  pp::PDF::Print(this);
 }
 
 void OutOfProcessInstance::SetContentRestrictions(int content_restrictions) {
@@ -1281,8 +1278,4 @@ void OutOfProcessInstance::UserMetricsRecordAction(const std::string& action) {
   pp::PDF::UserMetricsRecordAction(this, pp::Var(action));
 }
 
-void OutOfProcessInstance::OnPrint(int32_t /*unused_but_required*/) {
-  pp::PDF::Print(this);
-}
-
 }  // namespace chrome_pdf

pdf/out_of_process_instance.h

@@ -188,9 +188,6 @@ class OutOfProcessInstance : public PdfViewPluginBase,
   // Called after a preview page has loaded or failed to load.
   void LoadNextPreviewPage();
 
-  // Callback to print without re-entrancy issues.
-  void OnPrint(int32_t /*unused_but_required*/);
-
   // The Pepper image data that is in sync with mutable_image_data().
   pp::ImageData pepper_image_data_;