Include glGetMultisamplefv API

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1720963002

Committed: https://skia.googlesource.com/skia/+/69c1b24bcaa7cffd59753a75a7f3d155696fcac4

Review URL: https://codereview.chromium.org/1720963002
diff --git a/include/gpu/GrCaps.h b/include/gpu/GrCaps.h
index e2e44a5..60f2139 100644
--- a/include/gpu/GrCaps.h
+++ b/include/gpu/GrCaps.h
@@ -144,6 +144,7 @@
     bool compressedTexSubImageSupport() const { return fCompressedTexSubImageSupport; }
     bool oversizedStencilSupport() const { return fOversizedStencilSupport; }
     bool textureBarrierSupport() const { return fTextureBarrierSupport; }
+    bool sampleLocationsSupport() const { return fSampleLocationsSupport; }
     bool usesMixedSamples() const { return fUsesMixedSamples; }
 
     bool useDrawInsteadOfClear() const { return fUseDrawInsteadOfClear; }
@@ -276,6 +277,7 @@
     bool fCompressedTexSubImageSupport               : 1;
     bool fOversizedStencilSupport                    : 1;
     bool fTextureBarrierSupport                      : 1;
+    bool fSampleLocationsSupport                     : 1;
     bool fUsesMixedSamples                           : 1;
     bool fSupportsInstancedDraws                     : 1;
     bool fFullClearIsFree                            : 1;