Added a metric to check the number of extracted forms.

It is needed ro check the assumption that the data message received
and parsed on submission contains only one form at a time.

Change-Id: Ibb7af31e283bc67f40be1a46ad4bde4fb9763457
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2038572
Commit-Queue: Maria Kazinova <kazinova@google.com>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738922}

components/password_manager/ios/password_form_helper.mm

@@ -7,6 +7,7 @@
 #include <stddef.h>
 
 #include "base/bind.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/values.h"
 #include "components/autofill/core/common/form_data.h"
@@ -179,6 +180,8 @@ constexpr char kCommandPrefix[] = "passwordForm";
   NSString* nsFormData = [NSString stringWithUTF8String:formData.c_str()];
   autofill::ExtractFormsData(nsFormData, false, base::string16(), pageURL,
                              pageURL.GetOrigin(), &forms);
+  UMA_HISTOGRAM_EXACT_LINEAR("PasswordManager.NumFormsExtractedIOS",
+                             forms.size(), 50);
   if (forms.size() != 1)
     return;
   [self.delegate formHelper:self

tools/metrics/histograms/histograms.xml

@@ -112128,6 +112128,17 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="PasswordManager.NumFormsExtractedIOS" units="forms"
+    expires_after="2020-06-01">
+  <owner>dvadym@chromium.org</owner>
+  <owner>kazinova@google.com</owner>
+  <summary>
+    Records the number of password forms extracted by PasswordFormHelper at the
+    moment of submission. This metric is needed to check the assumption that
+    received and parsed message contains only one form at a a time.
+  </summary>
+</histogram>
+
 <histogram name="PasswordManager.NumPasswordsDeletedByBulkDelete" units="units"
     expires_after="M77">
   <obsolete>