Use glGetStringi to get extensions when available.

src/gpu/gl/GrGLDefines.h

Index: src/gpu/gl/GrGLDefines.h
===================================================================
--- src/gpu/gl/GrGLDefines.h	(revision 7868)
+++ src/gpu/gl/GrGLDefines.h	(working copy)
@@ -10,6 +10,11 @@
 #ifndef GrGLDefines_DEFINED
 #define GrGLDefines_DEFINED
 
+/* Profiles */
+#define GR_GL_CONTEXT_PROFILE_MASK              0x9126
+#define GR_GL_CONTEXT_CORE_PROFILE_BIT          0x00000001
+#define GR_GL_CONTEXT_COMPATIBILITY_PROFILE_BIT 0x00000002
+
 // The following constants consist of the intersection of GL constants
 // exported by GLES 1.0, GLES 2.0, and desktop GL required by the system.
 
@@ -356,6 +361,9 @@
 #define GR_GL_VERSION                        0x1F02
 #define GR_GL_EXTENSIONS                     0x1F03
 
+/* StringCounts */
+#define GR_GL_NUM_EXTENSIONS                 0x821D
+
 /* Pixel Mode / Transfer */
 #define GR_GL_UNPACK_ROW_LENGTH              0x0CF2
 #define GR_GL_PACK_ROW_LENGTH                0x0D02