Enable extension GL_ARB_fragment_coord_convention in FS. Speculative fix for Intel Win7 buildbots.

Unreviewed.

git-svn-id: http://skia.googlecode.com/svn/trunk@6032 2bbb7eff-a529-9590-31e7-b0007b416f81

src/gpu/gl/GrGLShaderBuilder.cpp

@@ -288,7 +288,8 @@ void GrGLShaderBuilder::addVarying(GrSLType type,
 const char* GrGLShaderBuilder::fragmentPosition() {
     if (fContext.caps().fragCoordConventionsSupport()) {
         if (!fSetupFragPosition) {
-            this->fFSHeader.append("layout(origin_upper_left) in vec4 gl_FragCoord;\n");
+            fFSHeader.printf("#extension GL_ARB_fragment_coord_convention: enable\n");
+            fFSHeader.append("layout(origin_upper_left) in vec4 gl_FragCoord;\n");
             fSetupFragPosition = true;
         }
         return "gl_FragCoord";