Isolate.spawnUri "checked" documentation needs some cleanup

[natebosch]

sdk/sdk/lib/isolate/isolate.dart

Lines 292 to 306 in 89edf64

	* If the [checked] parameter is set to `true` or `false`,
	* the new isolate will run code in checked mode (enabling asserts and type
	* checks), respectively in production mode (disabling asserts and type
	* checks), if possible. If the parameter is omitted, the new isolate will
	* inherit the value from the current isolate.
	*
	* In Dart2 strong mode, the `checked` parameter only controls asserts, but
	* not type checks.
	*
	* It may not always be possible to honor the `checked` parameter.
	* If the isolate code was pre-compiled, it may not be possible to change
	* the checked mode setting dynamically.
	* In that case, the `checked` parameter is ignored.
	*
	* WARNING: The [checked] parameter is not implemented on all platforms yet.

• We should drop "Dart 2 strong mode" - it is the only mode.
• The phrasing of the first sentence is very confusing.
• We should drop references to "type checks" since they are always enabled.
• What does "If this isolate code was pre-compiled". Does that refer to using a URI pointing to a kernel file?
• The warning about it not being supported on all platforms should be expanded. What platforms isn't is supported on? AOT?

[aam]

What does "If this isolate code was pre-compiled". Does that refer to using a URI pointing to a kernel file?

Yes. Assertions from dart code are included/dropped by the kernel compiler. If compilation was already done and VM spawnUri points at result kernel file, then this flag won't affect anything.

The warning about it not being supported on all platforms should be expanded. What platforms isn't is supported on? AOT?

Right, current limitations are:

• when targeting VM in AOT configuration you will get an Unsupported exception if you attempt to use spawnUri;
• when you target Web(using dart2js), then invocation of spawnUri in your dart app will result in UnsupportedError exception.

[natebosch]

when you target Web(using dart2js), then invocation of spawnUri in your dart app will result in UnsupportedError exception.

Our build system prevents importing dart:isolate on the web. These APIs should not be reachable with dart2js.