Add support for glMapBufferRange. Use glMapBufferRange and glMapBufferSubData.

src/gpu/gl/GrGLDefines.h

Index: src/gpu/gl/GrGLDefines.h
diff --git a/src/gpu/gl/GrGLDefines.h b/src/gpu/gl/GrGLDefines.h
index a4dc2f782b0eefb1a3322775c3f56cd2465212db..73f3d2e146e822ad40a4aa14ff4604f45c3e5674 100644
--- a/src/gpu/gl/GrGLDefines.h
+++ b/src/gpu/gl/GrGLDefines.h
@@ -601,6 +601,14 @@
 /* Vertex Buffer Object */
 #define GR_GL_WRITE_ONLY                         0x88B9
 #define GR_GL_BUFFER_MAPPED                      0x88BC
+
+#define GR_GL_MAP_READ_BIT                       0x0001
+#define GR_GL_MAP_WRITE_BIT                      0x0002
+#define GR_GL_MAP_INVALIDATE_RANGE_BIT           0x0004
+#define GR_GL_MAP_INVALIDATE_BUFFER_BIT          0x0008
+#define GR_GL_MAP_FLUSH_EXPLICIT_BIT             0x0010
+#define GR_GL_MAP_UNSYNCHRONIZED_BIT             0x0020
+
 /* Read Format */
 #define GR_GL_IMPLEMENTATION_COLOR_READ_TYPE   0x8B9A
 #define GR_GL_IMPLEMENTATION_COLOR_READ_FORMAT 0x8B9B