[mjsunit] Change assertThrows such that it can check the exception message.

Up until now assertThrows allows to check the type field of an
exception, which is, however, a custom field introduced in a single
regression test. With the change assertThrows allows to check the
message field of an exception, which is set for standard V8 exceptions
by default.

I use the new assertThrows to refactor test/mjsunit/wasm/divrem-trap.js

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2525313003
Cr-Commit-Position: refs/heads/master@{#41302}

test/mjsunit/mjsunit.js

@@ -376,7 +376,7 @@ var assertMatches;
         failWithMessage("invalid use of assertThrows, maybe you want assertThrowsEquals");
       }
       if (arguments.length >= 3) {
-        assertEquals(e.type, cause_opt);
+        assertEquals(e.message, cause_opt);
       }
       // Success.
       return;

test/mjsunit/regress/regress-2263.js

@@ -25,6 +25,30 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+assertThrows = function assertThrows(code, type_opt, cause_opt) {
+  var threwException = true;
+  try {
+    if (typeof code === 'function') {
+      code();
+    } else {
+      eval(code);
+    }
+    threwException = false;
+  } catch (e) {
+    if (typeof type_opt === 'function') {
+      assertInstanceof(e, type_opt);
+    } else if (type_opt !== void 0) {
+      failWithMessage("invalid use of assertThrows, maybe you want assertThrowsEquals");
+    }
+    if (arguments.length >= 3) {
+      assertEquals(e.type, cause_opt);
+    }
+    // Success.
+    return;
+  }
+  failWithMessage("Did not throw exception");
+};
+
 var obj = { length: { valueOf: function(){ throw { type: "length" }}}};
 var sep = { toString: function(){ throw { type: "toString" }}};
 assertThrows("Array.prototype.join.call(obj, sep)", undefined, "length");

test/mjsunit/wasm/divrem-trap.js

@@ -7,26 +7,8 @@
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
-function assertTraps(code, msg) {
-  var threwException = true;
-  try {
-    if (typeof code === 'function') {
-      code();
-    } else {
-      eval(code);
-    }
-    threwException = false;
-  } catch (e) {
-    if (typeof type_opt === 'function') {
-      assertInstanceof(e, type_opt);
-    }
-    if (arguments.length >= 3) {
-      assertEquals(e.type, cause_opt);
-    }
-    // Success.
-    return;
-  }
-  throw new MjsUnitAssertionError("Did not throw exception");
+var assertTraps = function(messageId, code) {
+  assertThrows(code, WebAssembly.RuntimeError, kTrapMsgs[messageId]);
 }