Add media router common classes and unittests.

chrome/browser/media/router/media_source_helper.cc

Index: chrome/browser/media/router/media_source_helper.cc
diff --git a/chrome/browser/media/router/media_source_helper.cc b/chrome/browser/media/router/media_source_helper.cc
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+++ b/chrome/browser/media/router/media_source_helper.cc
@@ -0,0 +1,52 @@
+// 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 "chrome/browser/media/router/media_source_helper.h"
+
+#include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
+#include "chrome/browser/media/router/media_source.h"
+#include "url/gurl.h"
+
+namespace media_router {
+
+// Prefixes used to format and detect various protocols' media source URNs.
+// See: https://www.ietf.org/rfc/rfc3406.txt
+const char kTabMediaUrnPrefix[] = "urn:x-org.chromium.media:source:tab";
+const char kDesktopMediaUrn[] = "urn:x-org.chromium.media:source:desktop";
+const char kCastUrnPrefix[] = "urn:x-com.google.cast:application:";
+
+MediaSource ForTabMediaSource(int tab_id) {
+  return MediaSource(base::StringPrintf("%s:%d", kTabMediaUrnPrefix, tab_id));
+}
+
+MediaSource ForDesktopMediaSource() {
+  return MediaSource(std::string(kDesktopMediaUrn));
+}
+
+// TODO(mfoltz): Remove when the TODO in
+// MediaSourceManager::GetDefaultMediaSource is resolved.
+MediaSource ForCastAppMediaSource(const std::string& app_id) {
+  return MediaSource(kCastUrnPrefix + app_id);
+}
+
+MediaSource ForPresentationUrl(const std::string& presentation_url) {
+  return MediaSource(presentation_url);
+}
+
+bool IsMirroringMediaSource(const MediaSource& source) {
+  return StartsWithASCII(source.id(), kDesktopMediaUrn, true) ||
+    StartsWithASCII(source.id(), kTabMediaUrnPrefix, true);
+}
+
+bool IsValidMediaSource(const MediaSource& source) {
+  if (IsMirroringMediaSource(source) ||
+      StartsWithASCII(source.id(), kCastUrnPrefix, true)) {
+    return true;
+  }
+  GURL url(source.id());
+  return url.is_valid() && url.SchemeIsHTTPOrHTTPS();
+}
+
+}  // namespace media_router