Include EXT_window_rectangles API

src/gpu/gl/GrGLInterface.cpp

Index: src/gpu/gl/GrGLInterface.cpp
diff --git a/src/gpu/gl/GrGLInterface.cpp b/src/gpu/gl/GrGLInterface.cpp
index d11a86b15a7503909d3a50c9bbd7b7a2ddbcd084..ada6d8bc298ce5c0411ac27222fa0b1c46705090 100644
--- a/src/gpu/gl/GrGLInterface.cpp
+++ b/src/gpu/gl/GrGLInterface.cpp
@@ -769,6 +769,12 @@ bool GrGLInterface::validate() const {
         }
     }
 
+    if (fExtensions.has("GL_EXT_window_rectangles")) {
+        if (nullptr == fFunctions.fWindowRectangles) {
+            RETURN_FALSE_INTERFACE
+        }
+    }
+
     if ((kGL_GrGLStandard == fStandard && glVer >= GR_GL_VER(4,0)) ||
         fExtensions.has("GL_ARB_sample_shading")) {
         if (nullptr == fFunctions.fMinSampleShading) {