fix for SkSL producing invalid branch after an OpKill

src/sksl/SkSLSPIRVCodeGenerator.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 "SkSLSPIRVCodeGenerator.h"
 
 #include "string.h"
@@ skipping 757 matching lines @@
             ABORT("unsupported SPIR-V op");    
     }
 }
 #endif
 
 void SPIRVCodeGenerator::writeOpCode(SpvOp_ opCode, int length, std::ostream& out) {
     ASSERT(opCode != SpvOpUndef);
     switch (opCode) {
         case SpvOpReturn:      // fall through
         case SpvOpReturnValue: // fall through
+        case SpvOpKill:        // fall through
         case SpvOpBranch:      // fall through
         case SpvOpBranchConditional:
             ASSERT(fCurrentBlock);
             fCurrentBlock = 0;
             break;
         case SpvOpConstant:          // fall through
         case SpvOpConstantTrue:      // fall through
         case SpvOpConstantFalse:     // fall through
         case SpvOpConstantComposite: // fall through
         case SpvOpTypeVoid:          // fall through
@@ skipping 1831 matching lines @@
     this->writeWord(SpvVersion, out);
     this->writeWord(SKSL_MAGIC, out);
     std::stringstream buffer;
     this->writeInstructions(program, buffer);
     this->writeWord(fIdCount, out);
     this->writeWord(0, out); // reserved, always zero
     out << buffer.str();
 }
 
 }