Add histogram for user activation in async clipboard API.

In this change, we are adding a histogram to see if sites are calling
async clipboard APIs without transient user activation. This will
help us determine whether we can make transient user activation a
strict requirement for async APIs regardless of what formats are
being read/written.
This will also help address the below github issue:
w3c/clipboard-apis#75 (comment)

Bug: 106449

Change-Id: I269eb69695a5d41b02db29732bab7144ffcfa8d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3650789
Reviewed-by: Austin Sullivan <[email protected]>
Reviewed-by: Stephen Chenney <[email protected]>
Commit-Queue: Anupam Snigdha <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1005514}
NOKEYCHECK=True
GitOrigin-RevId: 88afaabd3ee6e7413e379870c9cd7dba77e3353d

blink/renderer/modules/clipboard/clipboard_promise.cc

@@ -7,6 +7,7 @@
 #include <memory>
 #include <utility>
 
+#include "base/metrics/histogram_functions.h"
 #include "base/task/single_thread_task_runner.h"
 #include "mojo/public/cpp/base/big_buffer.h"
 #include "third_party/blink/public/common/features.h"
@@ -554,8 +555,11 @@ void ClipboardPromise::RequestPermission(
     return;
   }
 
-  if (!custom_format_items_.IsEmpty() &&
-      !LocalFrame::HasTransientUserActivation(GetLocalFrame())) {
+  bool has_transient_user_activation =
+      LocalFrame::HasTransientUserActivation(GetLocalFrame());
+  base::UmaHistogramBoolean("Blink.Clipboard.HasTransientUserActivation",
+                            has_transient_user_activation);
+  if (!custom_format_items_.IsEmpty() && !has_transient_user_activation) {
     script_promise_resolver_->Reject(MakeGarbageCollected<DOMException>(
         DOMExceptionCode::kSecurityError,
         "Must be handling a user gesture to use custom clipboard"));