Always support pack/unpack row length on ES3. Add support for NV_pack_subimage extension.

src/gpu/gl/GrGLCaps.cpp

Index: src/gpu/gl/GrGLCaps.cpp
===================================================================
--- src/gpu/gl/GrGLCaps.cpp	(revision 10767)
+++ src/gpu/gl/GrGLCaps.cpp	(working copy)
@@ -147,10 +147,11 @@
         fPackRowLengthSupport = true;
         fPackFlipYSupport = false;
     } else {
-        fUnpackRowLengthSupport =ctxInfo.hasExtension("GL_EXT_unpack_subimage");
+        fUnpackRowLengthSupport = version >= GR_GL_VER(3,0) ||
+                                  ctxInfo.hasExtension("GL_EXT_unpack_subimage");
         fUnpackFlipYSupport = ctxInfo.hasExtension("GL_CHROMIUM_flipy");
-        // no extension for pack row length
-        fPackRowLengthSupport = false;
+        fPackRowLengthSupport = version >= GR_GL_VER(3,0) ||
+                                ctxInfo.hasExtension("GL_NV_pack_subimage");
         fPackFlipYSupport =
             ctxInfo.hasExtension("GL_ANGLE_pack_reverse_row_order");
     }