Add function to GrProxyProvider to lazily upload mip map data

Bug: skia:
Change-Id: I906207727242bed8a109bf3ca10b5a6e8e4b952e
Reviewed-on: https://skia-review.googlesource.com/104581
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/gm/gamut.cpp b/gm/gamut.cpp
index c2303af..55f1b28 100644
--- a/gm/gamut.cpp
+++ b/gm/gamut.cpp
@@ -43,6 +43,7 @@
         int scaledSize = sk_float_round2int(scale * gRectSize);
         fBitmap.allocPixels(SkImageInfo::MakeS32(scaledSize, scaledSize, kPremul_SkAlphaType));
         fBitmap.eraseColor(color);
+        fBitmap.setImmutable();
         const char* qualityNames[] = { "None", "Low", "Medium", "High" };
         fLabel = SkStringPrintf("Bitmap (%s)", qualityNames[quality]);
     }