Add support to dart2js for option --enable-asserts.

tests/co19/co19-dart2js.status

Index: tests/co19/co19-dart2js.status
diff --git a/tests/co19/co19-dart2js.status b/tests/co19/co19-dart2js.status
index a9cfdf04a634014bd3eff6674edfc46b92c17477..83ce81d61b79c0509bd9e879360912948989b61e 100644
--- a/tests/co19/co19-dart2js.status
+++ b/tests/co19/co19-dart2js.status
@@ -374,6 +374,20 @@ LibTest/core/Map/Map_class_A01_t04: Slow, Pass # Please triage this failure
 LibTest/core/Uri/Uri_A06_t03: Slow, Pass # Please triage this failure
 LibTest/math/Point/operator_mult_A02_t01: RuntimeError # Issue 1533
 
+[ $compiler == dart2js && $enable_asserts ]

[sra1, 2017/05/24 01:30:46]

So the problem here is not that we have --enable-asserts, it is that we don't
have --checked (--enable-type-assertions).

Can we add something like !$checked to strengthen the condition.

If not, I would need a comment to say  $enable_asserts implies type assertions
are disabled to understand what is going on here.

[eernst, 2017/07/07 08:50:29]

$enable_asserts does not imply that type assertions are disabled, so this is a
problem. A similar situation exists in language/language-dart2js.status, but
when I fixed that I forgot to fix this one. Done.

+Language/Statements/Assert/execution_t01: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t02: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t03: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t04: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t05: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t06: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/execution_t11: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/production_mode_t01: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/type_t02: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/type_t03: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/type_t04: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/type_t05: SkipByDesign # Unspec'd feature.
+Language/Statements/Assert/type_t06: SkipByDesign # Unspec'd feature.
 
 [ $compiler == dart2js && $checked && $runtime != d8]
 LayoutTests/fast/canvas/webgl/framebuffer-object-attachment_t01: RuntimeError # Please triage this failure