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 d877267d28d90cf377bf8de8b0e4e0937bd09e8e..076236c74f0c15b6601791cfd4736f1ab130ea5b 100644
--- a/tests/co19/co19-dart2js.status
+++ b/tests/co19/co19-dart2js.status
@@ -376,6 +376,20 @@ 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 ]
+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