Add Generic Implementation of ClipboardRecentContent

components/open_from_clipboard/clipboard_recent_content.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/open_from_clipboard/clipboard_recent_content.h"
 
+#include "url/url_constants.h"
+
 namespace {
 ClipboardRecentContent* g_clipboard_recent_content = nullptr;
-}
+
+// Schemes appropriate for suggestion by ClipboardRecentContent.
+const char* kAuthorizedSchemes[] = {
+    url::kAboutScheme, url::kDataScheme, url::kHttpScheme, url::kHttpsScheme,
+    // TODO(mpearson): add support for chrome:// URLs.  Right now the scheme
+    // for that lives in content and is accessible via
+    // GetEmbedderRepresentationOfAboutScheme() or content::kChromeUIScheme
+    // TODO(mpearson): when adding desktop support, add kFileScheme, kFtpScheme,
+    // and kGopherScheme.
+};
+
+}  // namespace
 
 ClipboardRecentContent::ClipboardRecentContent() {}
 
-ClipboardRecentContent::~ClipboardRecentContent() {}
+ClipboardRecentContent::~ClipboardRecentContent() {
+  g_clipboard_recent_content = nullptr;

[Peter Kasting, 2017/04/03 23:35:18]

I'm still worried about lifetime management here.

Let's say we create one AutocompleteController, which creates a clipboard
instance and sets it as the default.  Then we create a second controller, which
does nothing because there's already an instance.  Then we destroy the first
controller.  This destroys the global instance.  Now the second controller can
remain alive, with no instance, for arbitrary time.

It seems like what you really want is either to have the ClipboardRecentContent
object be vended by a service factory, or have the one global instance be
refcounted, and have AutocompleteController take a scoped_refptr.

Also seems like maybe ClipboardRecentContent() should SetInstance()
automatically in the constructor if there is no current instance, rather than
exposing that publicly.

[Mark P, 2017/04/04 04:53:02]

Rightly so, you make a good point below.

I see two reasonable possibilities:
(i) set up a BrowserContextKeyedServiceFactory for ClipboardRecentContentGeneric
(ii) simply have a global single instance created on startup, a la iOS
https://cs.chromium.org/chromium/src/ios/chrome/browser/ios_chrome_main_parts...

(i) seems heavyweight but is probably the right thing to do for this generic
implementation.  Also, if choosing this path, we probably should convert the iOS
code to do the same thing.

(ii) seems easy and consistent with the iOS code.  Also, if choosing this path,
we should probably convert hte iOS code to delete the variable on shutdown. 
(Technically the variable is leaking.)

A third option, ref-counted pointers, seems notably worse than either of these.

+}
 
 // static
 ClipboardRecentContent* ClipboardRecentContent::GetInstance() {
   return g_clipboard_recent_content;
 }
 
 // static
 void ClipboardRecentContent::SetInstance(ClipboardRecentContent* instance) {
   g_clipboard_recent_content = instance;
 }
+
+// static
+bool ClipboardRecentContent::IsAppropriateSuggestion(const GURL& url) {
+  // Check to make sure it's a scheme we're willing to suggest.
+  for (const auto* authorized_scheme : kAuthorizedSchemes) {
+    if (url.SchemeIs(authorized_scheme))
+      return true;
+  }
+
+  // Not a scheme we're allowed to return.
+  return false;
+}