Fix range-based for loops which copy the loop variable unnecessarily.

This will allow us to enable the ClangTidy check
performance-for-range-copy.

Change-Id: I11f152ffe458f5f353da8715ffd2fd47cf4e71a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306946
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/gm/readpixels.cpp b/gm/readpixels.cpp
index 1fad98f..6095865 100644
--- a/gm/readpixels.cpp
+++ b/gm/readpixels.cpp
@@ -158,7 +158,7 @@
                 make_small_gamut(),
         };
 
-        for (sk_sp<SkColorSpace> dstColorSpace : colorSpaces) {
+        for (const sk_sp<SkColorSpace>& dstColorSpace : colorSpaces) {
             for (SkColorType srcColorType : colorTypes) {
                 canvas->save();
                 sk_sp<SkImage> image = make_raster_image(srcColorType);
@@ -227,7 +227,7 @@
         };
 
         sk_sp<SkImage> image = make_codec_image();
-        for (sk_sp<SkColorSpace> dstColorSpace : colorSpaces) {
+        for (const sk_sp<SkColorSpace>& dstColorSpace : colorSpaces) {
             canvas->save();
             for (SkColorType dstColorType : colorTypes) {
                 for (SkAlphaType dstAlphaType : alphaTypes) {
@@ -293,8 +293,8 @@
                 SkImage::kDisallow_CachingHint,
         };
 
-        for (sk_sp<SkImage> image : images) {
-            for (sk_sp<SkColorSpace> dstColorSpace : colorSpaces) {
+        for (const sk_sp<SkImage>& image : images) {
+            for (const sk_sp<SkColorSpace>& dstColorSpace : colorSpaces) {
                 canvas->save();
                 for (SkColorType dstColorType : colorTypes) {
                     for (SkAlphaType dstAlphaType : alphaTypes) {