add support for custom performance entries

[vigneshshanmugam]

What?

This PR adds the support for fragment teams to add custom metrics that looks similar to PerformanceEntry that can be retrieved via tailor in addition to the hooks it supports.

Pipe.addPerfEntry("time-to-meaningful-paint", 2000.00) // done from some fragment on some page

Pipe.getEntries()
// [{
   name: "time-to-meaningful-paint",
   duration: 2000.00,
   entryType: "tailor",
   startTime: // start time relative to navigation start
}]

Why?

Browsers right now does not expose an API for creating custom PerformanceEntry and make them available on PerformanceTimeline.

why not perfomance.measure(User Timing)?

• User Timing - mark and measure does not allow a way for pushing custom timing information. If you already have a metric and want to pass that information to PerformanceEntry you cannot do that right now with User Timing API.

why not extend PerformanceEntry?

Even if we hack and extend the PerformanceEntry object, there is no way to retrive the custom entries that are added.

var customEntry = {};
customEntry.prototype = PerformanceEntry;
customEntry.name = "ttfmp";
customEntry.duration = Number(paint); // custom paint timing
customEntry.entryType = "tailor";
customEntry.startTime = performance.now();


// retrive entries
performance.getEntries(); 
// returns []

Future

There is a existing issue and proposal in w3c web perf group on exposing the API. So once its landed, we can fallback to that or continue to use them for older browsers.
Issue - w3c/charter-webperf#28
Proposal - https://docs.google.com/document/d/1_zm9JB-Ul_fOtAMnF6yBcmvNL3m4-k4ram4pdMIcIug/

[codecov]

Codecov Report

Merging #187 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #187   +/-   ##
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  Coverage   98.29%   98.29%           
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  Files          14       14           
  Lines         586      586           
  Branches      104      104           
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  Hits          576      576           
  Misses         10       10

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[addityasingh]

👍

[DeTeam]

navigationStart is always available?

[vigneshshanmugam]

good catch, i forgot to add a check for navigation timing.

[vigneshshanmugam]

Fixed now, we should add the entry itself since it will result in skewed metrics.

[DeTeam]

👍

[vigneshshanmugam]

👍