Implement support for origin-TopLeft render targets in GL backend.

Review URL: https://codereview.appspot.com/7230049

git-svn-id: http://skia.googlecode.com/svn/trunk@7545 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLProgram.cpp b/src/gpu/gl/GrGLProgram.cpp
index 2aa7236..a4f0df2 100644
--- a/src/gpu/gl/GrGLProgram.cpp
+++ b/src/gpu/gl/GrGLProgram.cpp
@@ -64,6 +64,7 @@
 
     fViewMatrix = SkMatrix::InvalidMatrix();
     fViewportSize.set(-1, -1);
+    fOrigin = (GrSurfaceOrigin) -1;
     fColor = GrColor_ILLEGAL;
     fColorFilterColor = GrColor_ILLEGAL;
     fRTHeight = -1;