Rewrite YouTube Flash embeds

chrome/renderer/chrome_content_renderer_client.cc

Index: chrome/renderer/chrome_content_renderer_client.cc
diff --git a/chrome/renderer/chrome_content_renderer_client.cc b/chrome/renderer/chrome_content_renderer_client.cc
index 11fd9c54a74b045e7ae339dc5575504e89986da3..fb0c665961f17172aec8d86c08e48f78e1510cfd 100644
--- a/chrome/renderer/chrome_content_renderer_client.cc
+++ b/chrome/renderer/chrome_content_renderer_client.cc
@@ -21,6 +21,7 @@
 #include "base/values.h"
 #include "build/build_config.h"
 #include "chrome/common/channel_info.h"
+#include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_isolated_world_ids.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
@@ -1389,3 +1390,55 @@ bool ChromeContentRendererClient::ShouldEnforceWebRTCRoutingPreferences() {
   return true;
 #endif
 }
+
+GURL ChromeContentRendererClient::OverrideFlashEmbedWithHTML(const GURL& url) {
+  if (!base::FeatureList::IsEnabled(features::kOverrideYouTubeFlashEmbed))
+    return GURL();
+
+  if (!url.is_valid())
+    return GURL();
+
+  // We'll only modify YouTube Flash embeds. The URLs can be recognized since
+  // they're in the following form: youtube.com/v/VIDEO_ID. So, we check to see
+  // if the given URL does follow that format.
+  if (!url.DomainIs("youtube.com") || url.path().find("/v/") != 0)

[Mike West, 2016/08/04 12:41:38]

I'd suggest that we handle `youtube-nocookie.com` here as well.

Skimming through other browsers' code, WebKit handles this case
(https://github.com/WebKit/webkit/blob/master/Source/WebCore/Modules/plugins/Y...),
but Firefox doesn't
(http://searchfox.org/mozilla-central/source/dom/base/nsObjectLoadingContent.c...).
It might be worth filing a bug against Gecko to do the same. :)

WebKit also processes `youtu.be`, but that doesn't appear to redirect to Flash,
so I think we can safely ignore it here.

[kdsilva, 2016/08/05 11:06:02]

Done.

+    return GURL();
+
+  std::string url_str = url.spec();
+
+  // If the website is using an invalid YouTube URL, we'll try and
+  // fix the URL by ensuring that if there are multiple parameters,
+  // the parameter string begins with a "?" and then follows with a "&"
+  // for each subsequent parameter. We do this because the Flash video player
+  // has some URL correction capabilities so we don't want this move to HTML5
+  // to break webpages that used to work.
+  size_t index = url_str.find_first_of("&?");
+  bool invalid_url = index != std::string::npos && url_str.at(index) == '&';
+
+  if (invalid_url) {
+    // ? should appear first before all parameters
+    url_str.replace(index, 1, "?");
+
+    // Replace all instances of ? (after the first) with &
+    for (size_t pos = index + 1;
+        (pos = url_str.find("?",pos )) != std::string::npos; pos += 1)

[Mike West, 2016/08/04 12:41:38]

Nit: Please add braces here, as the for loop is multi-line. Also, the
indentation is a bit strange. Did `git cl format` produce this?

[kdsilva, 2016/08/05 11:06:02]

Done. Looks like `git cl format` did fix the indentation.

+      url_str.replace(pos, 1, "&");
+  }
+
+  GURL corrected_url = GURL(url_str);

[Mike West, 2016/08/04 12:41:38]

Nit: Did you consider wrapping this up in the `url::Replacement` bit below? That
is, creating a Replacements with the new path and query rather than reparsing
the URL?

[kdsilva, 2016/08/05 11:06:02]

Ack. 

+
+  // We don't modify any URLs that contain the enablejsapi=1 parameter
+  // since the page may be interacting with the YouTube Flash player in
+  // Javascript and we don't want to break working content.
+  if (corrected_url.query().find("enablejsapi=1") != std::string::npos)

[Mike West, 2016/08/04 12:41:38]

This will also match `?XXXenablejsapi=1` and `?a=enablejsapi=1` and
`?enablejsapi=100`. This might or might not matter, since we're dealing with the
pretty constrained world of YouTube embeds. *shrug*

[kdsilva, 2016/08/05 11:06:02]

Ack. Happy to discuss, but I think this is okay for our purposes. 

+    return GURL();
+
+  // Change the path to use the YouTube HTML5 API
+  std::string path = corrected_url.path();
+  path.replace(path.find("/v/"), 3, "/embed/");
+
+  url::Replacements<char> r;
+  r.SetPath(path.c_str(), url::Component(0, path.length()));
+
+  return corrected_url.ReplaceComponents(r);
+}