Complete remaining algo update_the_image_data
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script: A couple mutation observer fixes.
I felt like doing Servo stuff while trying to catch Gecko intermittents :)
This fixes most of #21233. I haven't dug into the other test.
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Rustfmt the constellation
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Yay for consistency!
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Merge run_wpt.py into run.py
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To ensure everything is still works, one can run `./mach test-wpt tests/wpt/mozilla/DOMParser.html`
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Track hash changes in session history
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Adds tracking of hash changes in the session history.
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Add some support for WPT tests in an Android emulator through WebDriver
This succeeds on my machine:
`./mach test-wpt --product servodriver --binary etc/run_in_headless_android_emulator.py --binary-arg servo-x86 --binary-arg target/i686-linux-android/release/servo.apk /_mozilla/mozilla/DOMParser.html`
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Implement step 5 of select_image_source
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This step is responsible for selecting an image source based on user agent's environment( closest value which is greater than user's pixel density)
In case of no device, maximum density source is selected.
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```
0:27.48 pid:4157 Traceback (most recent call last):
0:27.48 pid:4157 File "/home/simon/servo1/etc/run_in_headless_android_emulator.py", line 212, in <module>
0:27.48 pid:4157 sys.exit(main(*sys.argv[1:]))
0:27.48 pid:4157 File "/home/simon/servo1/etc/run_in_headless_android_emulator.py", line 72, in main
0:27.48 pid:4157 forward_webdriver(adb, args)
0:27.48 pid:4157 File "/home/simon/servo1/etc/run_in_headless_android_emulator.py", line 163, in forward_webdriver
0:27.48 pid:4157 ports = [int(part) for part in split if part]
0:27.48 pid:4157 ValueError: invalid literal for int() with base 10: 'None'
```
```
Traceback (most recent call last):
File "/home/simon/servo1/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/testrunner.py", line 90, in run
rv = commands[command](*args)
File "/home/simon/servo1/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/testrunner.py", line 110, in wait
self.executor.wait()
File "/home/simon/servo1/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/executors/base.py", line 209, in wait
self.protocol.base.wait()
AttributeError: 'ServoWebDriverProtocol' object has no attribute 'base'
```
When sending a webdriver load URL command soon enough after starting Servo,
that command could time out with a logged warning:
```
constellation: Webdriver load for closed browsing context (0,2).
```
When `closed` in this case really meant not opened yet.
Implement update source set & select image source
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- [x] These changes fix#11416 (github issue number if applicable).
- [x] These changes require tests but cannot be written until implementation of responsive images is complete
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