printing: Log when print preview is initiated

Add a new print preview event and log when print preview is initiated.

Bug: b:155084154
Change-Id: I400a97277b5c6d54c0221e52792b4e863feb81a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2168191
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763521}

components/printing/renderer/print_render_frame_helper.cc

@@ -92,10 +92,11 @@ STATIC_ASSERT_ENUM(blink::kWebLongEdge, LONG_EDGE);
 STATIC_ASSERT_ENUM(blink::kWebShortEdge, SHORT_EDGE);
 
 enum PrintPreviewHelperEvents {
-  PREVIEW_EVENT_REQUESTED,
-  PREVIEW_EVENT_CACHE_HIT,  // Unused
-  PREVIEW_EVENT_CREATE_DOCUMENT,
-  PREVIEW_EVENT_NEW_SETTINGS,  // Unused
+  PREVIEW_EVENT_REQUESTED,        // Received a request for a preview document.
+  PREVIEW_EVENT_CACHE_HIT,        // Unused.
+  PREVIEW_EVENT_CREATE_DOCUMENT,  // Started creating a preview document.
+  PREVIEW_EVENT_NEW_SETTINGS,     // Unused.
+  PREVIEW_EVENT_INITIATED,        // Initiated print preview.
   PREVIEW_EVENT_MAX,
 };
 
@@ -2387,6 +2388,11 @@ void PrintRenderFrameHelper::RequestPrintPreview(PrintPreviewRequestType type) {
       return;
     }
   }
+
+  base::UmaHistogramEnumeration(print_preview_context_.IsForArc()
+                                    ? "Arc.PrintPreview.PreviewEvent"
+                                    : "PrintPreview.PreviewEvent",
+                                PREVIEW_EVENT_INITIATED, PREVIEW_EVENT_MAX);
   Send(new PrintHostMsg_RequestPrintPreview(routing_id(), params));
 }
 

tools/metrics/histograms/enums.xml

@@ -54217,6 +54217,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="1" label="PREVIEW_EVENT_CACHE_HIT"/>
   <int value="2" label="PREVIEW_EVENT_CREATE_DOCUMENT"/>
   <int value="3" label="PREVIEW_EVENT_NEW_SETTINGS"/>
+  <int value="4" label="PREVIEW_EVENT_INITIATED"/>
 </enum>
 
 <enum name="PrintPreviewPdfActionBuckets">