Add MESA detection to GrContextInfo and use to decide whether to use GL_ALPHA or GL_RED.

src/gpu/gl/GrGLUtil.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 "GrGLUtil.h"
 
@@ skipping 103 matching lines @@
     }
 
     // check for ES2
     n = sscanf(versionString, "OpenGL ES %d.%d", &major, &minor);
     if (2 == n) {
         return kES2_GrGLBinding;
     }
     return kNone_GrGLBinding;
 }
 
+bool GrGLIsMesaFromVersionString(const char* versionString) {
+    int major, minor, mesaMajor, mesaMinor;
+    int n = sscanf(versionString, "%d.%d Mesa %d.%d", &major, &minor, &mesaMajor, &mesaMinor);
+    return 4 == n;
+}
+
 GrGLVersion GrGLGetVersionFromString(const char* versionString) {
     if (NULL == versionString) {
         GrAssert(!"NULL GL version string.");
         return 0;
     }
 
     int major, minor;
 
     // check for mesa
     int mesaMajor, mesaMinor;
@@ skipping 86 matching lines @@
     const GrGLubyte* v;
     GR_GL_CALL_RET(gl, v, GetString(GR_GL_SHADING_LANGUAGE_VERSION));
     return GrGLGetGLSLVersionFromString((const char*) v);
 }
 
 GrGLVendor GrGLGetVendor(const GrGLInterface* gl) {
     const GrGLubyte* v;
     GR_GL_CALL_RET(gl, v, GetString(GR_GL_VENDOR));
     return GrGLGetVendorFromString((const char*) v);
 }