Implement PrintBrowser functionality.

chrome/browser/printing/print_preview_message_handler.cc

Index: chrome/browser/printing/print_preview_message_handler.cc
diff --git a/chrome/browser/printing/print_preview_message_handler.cc b/chrome/browser/printing/print_preview_message_handler.cc
index 2ec09eb6df871bca49ab237a11e57bcdbe6a1000..26e74b05b5395ee7cb46b3b2a72e64d5daf3cae6 100644
--- a/chrome/browser/printing/print_preview_message_handler.cc
+++ b/chrome/browser/printing/print_preview_message_handler.cc
@@ -11,6 +11,7 @@
 #include <vector>
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/shared_memory.h"
@@ -18,8 +19,10 @@
 #include "chrome/browser/printing/print_job_manager.h"
 #include "chrome/browser/printing/print_preview_dialog_controller.h"
 #include "chrome/browser/printing/print_view_manager.h"
+#include "chrome/browser/printing/print_view_manager_common.h"
 #include "chrome/browser/printing/printer_query.h"
 #include "chrome/browser/ui/webui/print_preview/print_preview_ui.h"
+#include "chrome/common/chrome_switches.h"
 #include "components/printing/common/print_messages.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
@@ -243,4 +246,21 @@ bool PrintPreviewMessageHandler::OnMessageReceived(
   return handled;
 }
 
+#if BUILDFLAG(ENABLE_PRINT_BROWSER)
+// If PrintBrowser mode is enabled, trigger StartPrint() for every page
+void PrintPreviewMessageHandler::DidFinishLoad(

[skau, 2016/12/16 18:32:50]

This seems to have a limited relationship to PrintPreviewMessageHandler.  Does
this belong in a different class?

+    content::RenderFrameHost* render_frame_host,
+    const GURL& validated_url) {
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  bool print_browser_enabled =
+      command_line->HasSwitch(switches::kEnablePrintBrowser);
+  if (print_browser_enabled) {
+    content::WebContents* initiator =
+        content::WebContents::FromRenderFrameHost(render_frame_host);
+    printing::StartPrint(initiator, false /* print_preview_disabled */,

[skau, 2016/12/16 18:32:50]

You should enforce that Print Preview is enabled for Print Browser to be
enabled.  Otherwise, this could send a print job every time you load a page. 

[rbpotter, 2016/12/16 20:05:28]

In this case it may be implicitly enforced; I don't think
PrintPreviewMessageHandler gets created if Print Preview isn't enabled; it's
created in tab_helper.cc only if the ENABLE_PRINT_PREVIEW build flag is on.

+                         false /* has_selection */);
+  }
+}
+#endif
+
 }  // namespace printing