--gtest_filter does not work with earl grey tests as they are not based on gtest.
As they are based on XCUITests, they integrate nicely with Xcode test runner, so they easiest way to run a selected test is to generate Xcode project ("gn gen --ide=xcode --filters=//ios/chrome/* out/Debug-iphonesimulator"), open the Xcode project ("open out/Debug-iphonesimulator/all.xcworkspace"). Then in Xcode, select the test app you want to run, and in the Test navigator (the icon looks like a tilted square with a dash inside), select the test/test suite you want to run and click on the small arrow on its right.
Note that if you use src/ios/build/tools/setup-gn.py, then an Xcode project is already created in out/build/all.xcworkspace.
-- Sylvain