[android] Scan new credit card from autofill popup.

This patch adds a "Scan new card" menu item to the autofill popup on
Android. The feature is behind the command line flag:

  --enable-credit-card-scan

BUG=428085

Review URL: https://codereview.chromium.org/700623004

Cr-Commit-Position: refs/heads/master@{#305869}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index f7bbfd3..4d440a0 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2016,6 +2016,13 @@
     kOsAll,
     MULTI_VALUE_TYPE(kSSLVersionMinChoices)
   },
+  {
+    "enable-credit-card-scan",
+    IDS_FLAGS_ENABLE_CREDIT_CARD_SCAN_NAME,
+    IDS_FLAGS_ENABLE_CREDIT_CARD_SCAN_DESCRIPTION,
+    kOsAndroid,
+    SINGLE_VALUE_TYPE(autofill::switches::kEnableCreditCardScan)
+  },
   // NOTE: Adding new command-line switches requires adding corresponding
   // entries to enum "LoginCustomFlags" in histograms.xml. See note in
   // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.