Add support for glCompressedTexSubImage2D

R=bsalomon@google.com, robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/329213002
diff --git a/include/gpu/gl/GrGLFunctions.h b/include/gpu/gl/GrGLFunctions.h
index 51db053..5ac77a2 100644
--- a/include/gpu/gl/GrGLFunctions.h
+++ b/include/gpu/gl/GrGLFunctions.h
@@ -87,6 +87,7 @@
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLColorMaskProc)(GrGLboolean red, GrGLboolean green, GrGLboolean blue, GrGLboolean alpha);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCompileShaderProc)(GrGLuint shader);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCompressedTexImage2DProc)(GrGLenum target, GrGLint level, GrGLenum internalformat, GrGLsizei width, GrGLsizei height, GrGLint border, GrGLsizei imageSize, const GrGLvoid* data);
+    typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCompressedTexSubImage2DProc)(GrGLenum target, GrGLint level, GrGLint xoffset, GrGLint yoffset, GrGLsizei width, GrGLsizei height, GrGLenum format, GrGLsizei imageSize, const GrGLvoid* data);
     typedef GrGLvoid (GR_GL_FUNCTION_TYPE* GrGLCopyTexSubImage2DProc)(GrGLenum target, GrGLint level, GrGLint xoffset, GrGLint yoffset, GrGLint x, GrGLint y, GrGLsizei width, GrGLsizei height);
     typedef GrGLuint (GR_GL_FUNCTION_TYPE* GrGLCreateProgramProc)(void);
     typedef GrGLuint (GR_GL_FUNCTION_TYPE* GrGLCreateShaderProc)(GrGLenum type);
diff --git a/include/gpu/gl/GrGLInterface.h b/include/gpu/gl/GrGLInterface.h
index 2b33e8e..6c5ab24 100644
--- a/include/gpu/gl/GrGLInterface.h
+++ b/include/gpu/gl/GrGLInterface.h
@@ -168,6 +168,7 @@
         GLPtr<GrGLColorMaskProc> fColorMask;
         GLPtr<GrGLCompileShaderProc> fCompileShader;
         GLPtr<GrGLCompressedTexImage2DProc> fCompressedTexImage2D;
+        GLPtr<GrGLCompressedTexSubImage2DProc> fCompressedTexSubImage2D;
         GLPtr<GrGLCopyTexSubImage2DProc> fCopyTexSubImage2D;
         GLPtr<GrGLCreateProgramProc> fCreateProgram;
         GLPtr<GrGLCreateShaderProc> fCreateShader;