[Async Clipboard API] Add histogram for empty clipboard.

Record when an empty clipboard is encountered during `read()`.

Gathering data for w3c/clipboard-apis#179.

Bug: 1500440

Change-Id: I7c9c162ec7e17ea18a42683c9720330cbac57b3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5029806
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Anupam Snigdha <snianu@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1225837}

content/browser/renderer_host/clipboard_host_impl_browsertest.cc

@@ -8,6 +8,7 @@
 #include "base/base_paths.h"
 #include "base/files/file_util.h"
 #include "base/path_service.h"
+#include "base/test/metrics/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/threading/thread_restrictions.h"
 #include "content/public/browser/browser_context.h"
@@ -181,4 +182,42 @@ IN_PROC_BROWSER_TEST_P(ClipboardDocUrlBrowserTestP, HtmlUrl) {
   EXPECT_EQ(src_url, main_url.spec());
 }
 
+class ClipboardBrowserTest : public ClipboardHostImplBrowserTest {
+ public:
+  ClipboardBrowserTest() = default;
+};
+
+IN_PROC_BROWSER_TEST_F(ClipboardBrowserTest, EmptyClipboard) {
+  base::HistogramTester histogram_tester;
+  GURL main_url(embedded_test_server()->GetURL("/title1.html"));
+  ASSERT_TRUE(NavigateToURL(shell(), main_url));
+  PermissionController* permission_controller =
+      GetRenderFrameHost()->GetBrowserContext()->GetPermissionController();
+  url::Origin origin = url::Origin::Create(main_url);
+  SetPermissionControllerOverrideForDevTools(
+      permission_controller, origin,
+      blink::PermissionType::CLIPBOARD_READ_WRITE,
+      blink::mojom::PermissionStatus::GRANTED);
+  ui::Clipboard::GetForCurrentThread()->Clear(ui::ClipboardBuffer::kCopyPaste);
+  // Currently we throw an exception if the clipboard is empty.
+  ASSERT_FALSE(ExecJs(shell(), " navigator.clipboard.read()"));
+  SetPermissionControllerOverrideForDevTools(
+      permission_controller, origin,
+      blink::PermissionType::CLIPBOARD_SANITIZED_WRITE,
+      blink::mojom::PermissionStatus::GRANTED);
+  ASSERT_TRUE(ExecJs(
+      shell(),
+      " const format1 = 'text/html';"
+      " const textInput = '<p>Hello</p>';"
+      " const blobInput1 = new Blob([textInput], {type: format1});"
+      " const clipboardItemInput = new ClipboardItem({[format1]: blobInput1});"
+      " navigator.clipboard.write([clipboardItemInput]);"));
+  ASSERT_TRUE(ExecJs(shell(), " navigator.clipboard.read()"));
+  content::FetchHistogramsFromChildProcesses();
+  histogram_tester.ExpectBucketCount("Blink.Clipboard.Read.NumberOfFormats", 0,
+                                     1);
+  histogram_tester.ExpectBucketCount("Blink.Clipboard.Read.NumberOfFormats", 1,
+                                     1);
+}
+
 }  // namespace content

third_party/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"
@@ -351,6 +352,8 @@ void ClipboardPromise::ResolveRead() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(GetExecutionContext());
 
+  base::UmaHistogramCounts100("Blink.Clipboard.Read.NumberOfFormats",
+                              clipboard_item_data_.size());
   if (!clipboard_item_data_.size()) {
     script_promise_resolver_->Reject(MakeGarbageCollected<DOMException>(
         DOMExceptionCode::kDataError, "No valid data on clipboard."));

tools/metrics/histograms/metadata/blink/histograms.xml

@@ -684,6 +684,17 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram name="Blink.Clipboard.Read.NumberOfFormats" units="count"
+    expires_after="2024-03-31">
+  <owner>estade@chromium.org</owner>
+  <owner>storage-dev@chromium.org</owner>
+  <owner>snianu@microsoft.com</owner>
+  <summary>
+    Reports the number of formats read from the system clipboard when
+    navigator.clipboard.read() is called.
+  </summary>
+</histogram>
+
 <histogram name="Blink.ColorGamut.Destination" enum="Gamut" expires_after="M85">
   <owner>brianosman@chromium.org</owner>
   <owner>mcasas@google.com</owner>