Add common page filtering logic for page load metrics.

chrome/common/page_load_metrics/page_tracker_predicate.h

+// Copyright 2016 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.
+
+#ifndef CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_TRACKER_PREDICATE_H_
+#define CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_TRACKER_PREDICATE_H_
+
+#include "base/macros.h"
+
+namespace page_load_metrics {
+
+// PageTrackerPredicate is an interface used to determine whether metrics should
+// be tracked for a given page. Consumers should call ShouldTrackPage() to
+// determine if a page load should be tracked. Implementers should implement the
+// pure virtual methods to provide information needed about the current page
+// load to determine if it should be tracked.
+class PageTrackerPredicate {

[Charlie Harrison, 2016/09/13 17:51:04]

Calling a class a predicate doesn't really sit well with me. Isn't a predicate
usually a function?

[Bryan McQuade, 2016/09/13 17:59:09]

Yeah, I agree - it's not my favorite name either, but I couldn't think of a
better name here. What else might we call it. I do think a predicate is usually
a function, or 'function object' which exposes a virtual boolean method to be
invoked. Here's one example:
https://cs.chromium.org/chromium/src/chrome/browser/extensions/api/declarativ...

+ public:
+  PageTrackerPredicate();
+  virtual ~PageTrackerPredicate();
+
+  // Whether metrics should be tracked for the current page.
+  bool ShouldTrackPage();
+
+  // Whether the navigation for the current page has committed.
+  virtual bool HasCommitted() = 0;
+
+  // Whether the current page's URL is HTTP or HTTPS. Note that the page does
+  // not need to have committed, nor does the URL or hostname of the URL need to
+  // point at a valid web page or host, for this method to return true.
+  virtual bool IsHTTPOrHTTPSUrl() = 0;
+
+  // Whether the current page's URL is for a Chrome new tab page. Note that in
+  // some cases the new tab page is served over the network via https.
+  virtual bool IsNewTabPageUrl() = 0;
+
+  // The methods below can only be called if HasCommitted() returns true.
+
+  // Whether the current page is a Chrome-generated error page. Example error
+  // pages include pages displayed after a network error that did not result in
+  // receiving an HTTP/HTTPS response, such as the 'There is no Internet
+  // connection' page, which is displayed when the user attempts to navigate
+  // without an Internet connection. This method returns false for non-Chrome
+  // generated error pages, such as pages with 4xx/5xx response codes. To
+  // check whether the current page resulted in a 4xx/5xx error, use
+  // IsNetworkErrorPage() instead.
+  virtual bool IsChromeErrorPage() = 0;
+
+  // Whether the current page is an HTTP(S) error page received over the
+  // network, such as a page with a 4xx/5xx response code.
+  virtual bool IsNetworkErrorPage() = 0;

[Bryan McQuade, 2016/09/13 17:39:21]

perhaps this should be called 'IsHTTPErrorPage'? I hesitated there only because
readers might get confused as to whether it's HTTP specific (not HTTPS) - do you
think that's a concern? Which name do you prefer?

[Charlie Harrison, 2016/09/13 17:51:04]

Go with HTTP. You could even be more verbose: "IsHTTP2XXOr3XXResponse".

+
+  // Whether the current page is an HTML or XHTML page.
+  virtual bool IsHTMLOrXHTMLPage() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PageTrackerPredicate);
+};
+
+}  // namespace page_load_metrics
+
+#endif  // CHROME_COMMON_PAGE_LOAD_METRICS_PAGE_TRACKER_PREDICATE_H_