Disable dual source blending support when GLSL version is too old

src/gpu/gl/GrGLSL.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLSL.h"
 #include "GrGLShaderVar.h"
 #include "SkString.h"
@@ skipping 67 matching lines @@
                 SkASSERT(kGL_GrGLStandard == info.standard());
                 if (info.caps()->isCoreProfile()) {
                     return "#version 330\n";
                 } else {
                     return "#version 330 compatibility\n";
                 }
             }
         case k310es_GrGLSLGeneration:
             SkASSERT(kGLES_GrGLStandard == info.standard());
             return "#version 310 es\n";
-        default:
-            SkFAIL("Unknown GL version.");
-            return ""; // suppress warning
     }
+    return "<no version>";
+}
+
+bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration gen) {
+    switch (gen) {
+        case k110_GrGLSLGeneration:
+            return false;
+        case k130_GrGLSLGeneration:
+        case k140_GrGLSLGeneration:
+        case k150_GrGLSLGeneration:
+        case k330_GrGLSLGeneration:
+        case k310es_GrGLSLGeneration:
+            return true;
+    }
+    return false;
 }
 
 void GrGLSLAppendDefaultFloatPrecisionDeclaration(GrSLPrecision p, GrGLStandard s, SkString* out) {
     // Desktop GLSL has added precision qualifiers but they don't do anything.
     if (kGLES_GrGLStandard == s) {
         switch (p) {
             case kHigh_GrSLPrecision:
                 out->append("precision highp float;\n");
                 break;
             case kMedium_GrSLPrecision:
@@ skipping 12 matching lines @@
     if (mulFactor.isOnes()) {
         *outAppend = SkString();
     }
 
     if (mulFactor.isZeros()) {
         outAppend->appendf("%s = vec4(0);", vec4VarName);
     } else {
         outAppend->appendf("%s *= %s;", vec4VarName, mulFactor.c_str());
     }
 }