Clipboard: Add UMA metrics for content script reads without user activation.

The proportion of content script reads without user activation will
inform potential deprecation plan and messaging.

Bug: 1051198
Change-Id: Ie9c76a6d26ee78219729ef54da7237eb061c98f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2440116Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813889}

chrome/renderer/chrome_content_settings_agent_delegate.cc

@@ -12,6 +12,7 @@
 #include "third_party/blink/public/web/web_local_frame.h"
 
 #if BUILDFLAG(ENABLE_EXTENSIONS)
+#include "base/metrics/histogram_functions.h"
 #include "extensions/common/constants.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/permissions/api_permission.h"
@@ -73,6 +74,16 @@ ChromeContentSettingsAgentDelegate::AllowReadFromClipboard() {
       extension_dispatcher_->script_context_set().GetCurrent();
   if (current_context && current_context->HasAPIPermission(
                              extensions::APIPermission::kClipboardRead)) {
+    if (current_context->context_type() ==
+        extensions::Feature::CONTENT_SCRIPT_CONTEXT) {
+      bool has_user_activation =
+          render_frame_->GetWebFrame()->HasTransientUserActivation();
+      // TODO(https://crbug.com/1051198): Evaluate and deprecate content script
+      // read without user activation after enough data is gathered.
+      base::UmaHistogramBoolean(
+          "Clipboard.ExtensionContentScriptReadHasUserActivation",
+          has_user_activation);
+    }
     return true;
   }
 #endif

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -2245,6 +2245,16 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Clipboard.ExtensionContentScriptReadHasUserActivation"
+    units="proportion" expires_after="2021-04-01">
+  <owner>huangdarwin@chromium.org</owner>
+  <owner>src/third_party/blink/renderer/modules/clipboard/OWNERS</owner>
+  <summary>
+    For calls to document.execCommand('paste') by extensions via content
+    scripts, record the proportion of calls with user activation.
+  </summary>
+</histogram>
+
 <histogram name="Clipboard.Read" enum="ClipboardFormatRead"
     expires_after="2021-03-07">
   <owner>huangdarwin@chromium.org</owner>