Fail to create GrContext when we get a NULL for a GL/GLSL version string

src/gpu/gl/GrGLSL.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLSL_DEFINED
 #define GrGLSL_DEFINED
 
@@ skipping 22 matching lines @@
     k140_GrGLSLGeneration,
     /**
      * Desktop GLSL 1.50
      */
     k150_GrGLSLGeneration,
 };
 
 /**
  * Gets the most recent GLSL Generation compatible with the OpenGL context.
  */
-GrGLSLGeneration GrGetGLSLGeneration(const GrGLInterface* gl);
+bool GrGetGLSLGeneration(const GrGLInterface* gl, GrGLSLGeneration* generation);
 
 /**
  * Returns a string to include at the beginning of a shader to declare the GLSL
  * version.
  */
 const char* GrGetGLSLVersionDecl(const GrGLContextInfo&);
 
 /**
  * Converts a GrSLType to a string containing the name of the equivalent GLSL type.
  */
@@ skipping 257 matching lines @@
 /**
  * Does an inplace mul, *=, of vec4VarName by mulFactor.
  * A semicolon and newline are added after the assignment.
  */
 void GrGLSLMulVarBy4f(SkString* outAppend, unsigned tabCnt,
                       const char* vec4VarName, const GrGLSLExpr4& mulFactor);
 
 #include "GrGLSL_impl.h"
 
 #endif