Add metrics for triggering of JS dialogs on Android.

chrome/browser/ui/android/javascript_app_modal_dialog_android.cc

Index: chrome/browser/ui/android/javascript_app_modal_dialog_android.cc
diff --git a/chrome/browser/ui/android/javascript_app_modal_dialog_android.cc b/chrome/browser/ui/android/javascript_app_modal_dialog_android.cc
index 3c82caff4c1cdfd9f6084a63d2aea66ef6ddf6e6..5f7a18f5540b11029939a7106022efc5b67c769e 100644
--- a/chrome/browser/ui/android/javascript_app_modal_dialog_android.cc
+++ b/chrome/browser/ui/android/javascript_app_modal_dialog_android.cc
@@ -8,6 +8,8 @@
 #include "base/android/jni_string.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
+#include "chrome/browser/android/tab_android.h"
 #include "chrome/browser/ui/javascript_dialogs/chrome_javascript_native_dialog_factory.h"
 #include "components/app_modal/app_modal_dialog_queue.h"
 #include "components/app_modal/javascript_app_modal_dialog.h"
@@ -46,7 +48,9 @@ void JavascriptAppModalDialogAndroid::ShowAppModalDialog() {
   // Keep a strong ref to the parent window while we make the call to java to
   // display the dialog.
   ScopedJavaLocalRef<jobject> parent_jobj = parent_jobject_weak_ref_.get(env);
-  if (parent_jobj.is_null()) {
+
+  TabAndroid* tab = TabAndroid::FromWebContents(dialog_->web_contents());
+  if (parent_jobj.is_null() || !tab) {
     CancelAppModalDialog();
     return;
   }
@@ -57,13 +61,16 @@ void JavascriptAppModalDialogAndroid::ShowAppModalDialog() {
   ScopedJavaLocalRef<jstring> message =
       ConvertUTF16ToJavaString(env, dialog_->message_text());
 
+  bool foremost = tab->IsUserInteractable();
   switch (dialog_->javascript_message_type()) {
     case content::JAVASCRIPT_MESSAGE_TYPE_ALERT: {
+      UMA_HISTOGRAM_BOOLEAN("JSDialogs.IsForemost.Alert", foremost);
       dialog_object = Java_JavascriptAppModalDialog_createAlertDialog(
           env, title, message, dialog_->display_suppress_checkbox());
       break;
     }
     case content::JAVASCRIPT_MESSAGE_TYPE_CONFIRM: {
+      UMA_HISTOGRAM_BOOLEAN("JSDialogs.IsForemost.Confirm", foremost);
       if (dialog_->is_before_unload_dialog()) {
         dialog_object = Java_JavascriptAppModalDialog_createBeforeUnloadDialog(

[Ted C, 2017/01/12 01:11:39]

@avi: are beforeunload handlers triggered differently on desktop?  should we
only log the above for the else case?

[Avi (use Gerrit), 2017/01/12 01:25:38]

beforeunload is a different code path on desktop; this is used only for
window.confirm. Definitely the else path here.

[Ted C, 2017/01/13 17:32:05]

Moved to the else

             env, title, message, dialog_->is_reload(),
@@ -75,6 +82,7 @@ void JavascriptAppModalDialogAndroid::ShowAppModalDialog() {
       break;
     }
     case content::JAVASCRIPT_MESSAGE_TYPE_PROMPT: {
+      UMA_HISTOGRAM_BOOLEAN("JSDialogs.IsForemost.Prompt", foremost);
       ScopedJavaLocalRef<jstring> default_prompt_text =
           ConvertUTF16ToJavaString(env, dialog_->default_prompt_text());
       dialog_object = Java_JavascriptAppModalDialog_createPromptDialog(