Implementing comma operator for asm->wasm.

BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=mjsunit/asm-wasm
R=aseemgarg@chromium.org,titzer@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1704553002

Cr-Commit-Position: refs/heads/master@{#34044}

src/wasm/asm-wasm-builder.cc

@@ -1026,6 +1026,10 @@ class AsmWasmBuilderImpl : public AstVisitor {
           }
           break;
         }
+        case Token::COMMA: {
+          current_function_builder_->EmitWithU8(kExprBlock, 2);
+          break;
+        }
         default:
           UNREACHABLE();
       }

test/mjsunit/wasm/asm-wasm.js

@@ -1042,6 +1042,7 @@ function TestForeignFunctions() {
 
 TestForeignFunctions();
 
+
 function TestForeignFunctionMultipleUse() {
   function AsmModule(stdlib, foreign, buffer) {
     "use asm";
@@ -1219,3 +1220,28 @@ TestForeignVariables();
   assertEquals(42, m.iload(4));
   assertEquals(77, m.iload(8));
 })();
+
+
+(function TestComma() {
+  function CommaModule() {
+    "use asm";
+
+    function ifunc(a, b) {
+      a = +a;
+      b = b | 0;
+      return (a, b) | 0;
+    }
+
+    function dfunc(a, b) {
+      a = a | 0;
+      b = +b;
+      return +(a, b);
+    }
+
+    return {ifunc: ifunc, dfunc: dfunc};
+  }
+
+  var m = _WASMEXP_.instantiateModuleFromAsm(CommaModule.toString());
+  assertEquals(123, m.ifunc(456.7, 123));
+  assertEquals(123.4, m.dfunc(456, 123.4));
+})();