[LSC] Replace base::string16 in //components/{omnibox,password_manager}

This change replaces base::string16 with std::u16string in
//components/omnibox and //components/password_manager.

Reproduction steps:
$ git grep -lw 'base::string16' components/{omnibox,password_manager} \
      | xargs sed -i 's/\bbase::string16\b/std::u16string/g'
$ git cl format

Bug: 1184339
Change-Id: I074b918355ad76537460b4623efe856f94886773
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2751106
Auto-Submit: Jan Wilken Dörrie <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Owners-Override: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#862296}
diff --git a/components/omnibox/browser/clipboard_provider.cc b/components/omnibox/browser/clipboard_provider.cc
index 0078dab..b19ad9c 100644
--- a/components/omnibox/browser/clipboard_provider.cc
+++ b/components/omnibox/browser/clipboard_provider.cc
@@ -250,10 +250,10 @@
   // If the omnibox is not empty, add a default match.
   // This match will be opened when the user presses "Enter".
   if (!input.text().empty()) {
-    const base::string16 description =
+    const std::u16string description =
         (base::FeatureList::IsEnabled(omnibox::kDisplayTitleForCurrentUrl))
             ? input.current_title()
-            : base::string16();
+            : std::u16string();
     AutocompleteMatch verbatim_match = VerbatimMatchForURL(
         this, client_, input, input.current_url(), description, -1);
     matches_.push_back(verbatim_match);
@@ -362,13 +362,13 @@
     const AutocompleteInput& input,
     bool* read_clipboard_content) {
   *read_clipboard_content = false;
-  base::Optional<base::string16> optional_text =
+  base::Optional<std::u16string> optional_text =
       clipboard_content_->GetRecentTextFromClipboard();
   if (!optional_text)
     return base::nullopt;
 
   *read_clipboard_content = true;
-  base::string16 text = std::move(optional_text).value();
+  std::u16string text = std::move(optional_text).value();
 
   // The clipboard can contain the empty string, which shouldn't be suggested.
   if (text.empty())
@@ -475,7 +475,7 @@
 }
 
 base::Optional<AutocompleteMatch> ClipboardProvider::NewClipboardTextMatch(
-    base::string16 text) {
+    std::u16string text) {
   // The text in the clipboard is a url. We don't want to prompt the user to
   // search for a url.
   if (GURL(text).is_valid())