added constant folding & branch elimination to skslc

tests/SkSLErrorTest.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkSLCompiler.h"
 
 #include "Test.h"
@@ skipping 334 matching lines @@
     test_failure(r,
                  "void foo() { while(true) {} if (true) break; }",
                  "error: 1: break statement must be inside a loop\n1 error\n");
 }
 
 DEF_TEST(SkSLContinueOutsideLoop, r) {
     test_failure(r,
                  "void foo() { for(;;); continue; }",
                  "error: 1: continue statement must be inside a loop\n1 error\n");
 }
+
+DEF_TEST(SkSLStaticIfError, r) {
+    // ensure eliminated branch of static if / ternary is still checked for errors
+    test_failure(r,
+                 "void foo() { if (true); else x = 5; }",
+                 "error: 1: unknown identifier 'x'\n1 error\n");
+    test_failure(r,
+                 "void foo() { if (false) x = 5; }",
+                 "error: 1: unknown identifier 'x'\n1 error\n");
+    test_failure(r,
+                 "void foo() { true ? 5 : x; }",
+                 "error: 1: unknown identifier 'x'\n1 error\n");
+    test_failure(r,
+                 "void foo() { false ? x : 5; }",
+                 "error: 1: unknown identifier 'x'\n1 error\n");
+}