Get correct GLVersion for Mesa to avoid GrContext creation failure

src/gpu/gl/GrGLUtil.cpp

Index: src/gpu/gl/GrGLUtil.cpp
===================================================================
--- src/gpu/gl/GrGLUtil.cpp	(revision 9286)
+++ src/gpu/gl/GrGLUtil.cpp	(working copy)
@@ -48,6 +48,37 @@
     }
 }
 
+namespace {
+bool get_gl_version_for_mesa(const int mesaMajorVersion,
+                             int* major,
+                             int* minor) {
+    switch (mesaMajorVersion) {
+        case 2:
+        case 3:
+        case 4:
+        case 5:
+        case 6:
+            *major = 1;
+            *minor = mesaMajorVersion - 1;
+            return true;
+        case 7:
+            *major = 2;
+            *minor = 1;
+            return true;
+        case 8:
+            *major = 3;
+            *minor = 0;
+            return true;
+        case 9:
+            *major = 3;
+            *minor = 1;
+            return true;
+        default:
+            return false;
+    }
+}
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #if GR_GL_LOG_CALLS
@@ -99,7 +130,19 @@
 
     int major, minor;
 
-    int n = sscanf(versionString, "%d.%d", &major, &minor);
+    // check for mesa
+    int mesaMajor, mesaMinor;
+    int n = sscanf(versionString, "%d.%d Mesa %d.%d", &major, &minor,
+                                                     &mesaMajor, &mesaMinor);
+    if (4 == n) {
+        if (get_gl_version_for_mesa(mesaMajor, &major, &minor)) {
+            return GR_GL_VER(major, minor);
+        } else {
+            return 0;
+        }
+    }
+
+    n = sscanf(versionString, "%d.%d", &major, &minor);
     if (2 == n) {
         return GR_GL_VER(major, minor);
     }