Add Generic Implementation of ClipboardRecentContent

components/omnibox/browser/autocomplete_controller.cc

Index: components/omnibox/browser/autocomplete_controller.cc
diff --git a/components/omnibox/browser/autocomplete_controller.cc b/components/omnibox/browser/autocomplete_controller.cc
index 1a175d428d4d3b574c6fcf544b923948eb85d461..9ab05f7592a36bfb822d7cfad874637a995ab03f 100644
--- a/components/omnibox/browser/autocomplete_controller.cc
+++ b/components/omnibox/browser/autocomplete_controller.cc
@@ -31,6 +31,7 @@
 #include "components/omnibox/browser/shortcuts_provider.h"
 #include "components/omnibox/browser/zero_suggest_provider.h"
 #include "components/open_from_clipboard/clipboard_recent_content.h"
+#include "components/open_from_clipboard/clipboard_recent_content_generic.h"
 #include "components/search_engines/template_url.h"
 #include "components/search_engines/template_url_service.h"
 #include "components/strings/grit/components_strings.h"
@@ -231,6 +232,15 @@ AutocompleteController::AutocompleteController(
   if (provider_types & AutocompleteProvider::TYPE_CLIPBOARD_URL) {
     ClipboardRecentContent* clipboard_recent_content =
         ClipboardRecentContent::GetInstance();
+    // On iOS, a global ClipboardRecentContent should've been created by now
+    // (if enabled).  If none has been created (e.g., we're on a different
+    // platform), use the generic implementation, which AutocompleteController
+    // will own.
+    if (!clipboard_recent_content) {
+      clipboard_recent_content_.reset(new ClipboardRecentContentGeneric());

[Peter Kasting, 2017/04/01 05:54:28]

Nit: Prefer =MakeUnique to reset(new

[Mark P, 2017/04/02 05:33:56]

Done.

+      ClipboardRecentContent::SetInstance(clipboard_recent_content_.get());
+      clipboard_recent_content = clipboard_recent_content_.get();
+    }
     if (clipboard_recent_content) {

[Peter Kasting, 2017/04/01 05:54:28]

It seems like this can't fail now and can be removed.

Nit: In which case we could eliminate the temp because it's more trouble than
it's worth:

    if (!ClipboardRecentContent::GetInstance()) {
      ...
    }
    ...use ClipboardRecentContent::GetInstance() directly

[Mark P, 2017/04/02 05:33:56]

Yeah, I agree that it's more trouble than it's worth.  Done.  Thanks for
pointing out the obvious above (that the creation can't fail), which thus makes
it easy to use ClipboardRecentContent::GetInstance() where needed.  (Otherwise
the repeated ClipboardRecentContent::GetInstance() looked like a pain.)

       providers_.push_back(new ClipboardURLProvider(provider_client_.get(),
                                                     history_url_provider_,