Cleanup: Get rid of make_isize() function from gm.h.

This helper function is not necessary.

The same thing can be achieved by using SkISize::Make() provided by
SkTSize API.

BUG=skia:2645
TEST=make dm && out/Debug/dm
R=robertphillips@google.com, reed@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/326523002
diff --git a/gm/rrects.cpp b/gm/rrects.cpp
index 8e4b199..24636ca 100644
--- a/gm/rrects.cpp
+++ b/gm/rrects.cpp
@@ -54,7 +54,7 @@
         return name;
     }
 
-    virtual SkISize onISize() SK_OVERRIDE { return make_isize(kImageWidth, kImageHeight); }
+    virtual SkISize onISize() SK_OVERRIDE { return SkISize::Make(kImageWidth, kImageHeight); }
 
     virtual uint32_t onGetFlags() const SK_OVERRIDE {
         if (kEffect_Type == fType) {