Add glReadBuffer to GrGLInterface.

Review URL: http://codereview.appspot.com/4841048/





git-svn-id: http://skia.googlecode.com/svn/trunk@2034 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/src/GrGLInterface.cpp b/gpu/src/GrGLInterface.cpp
index 9822dcb..2a8ffaa 100644
--- a/gpu/src/GrGLInterface.cpp
+++ b/gpu/src/GrGLInterface.cpp
@@ -313,7 +313,8 @@
     if (kDesktop_GrGLBinding == fBindingsExported &&
         (NULL == fLineWidth ||
          NULL == fGetTexLevelParameteriv ||
-         NULL == fDrawBuffer)) {
+         NULL == fDrawBuffer ||
+         NULL == fReadBuffer)) {
         return false;
     }