Add GrContext.h #include to viz/common/skia_helper.cc

An upcoming Skia CL (see below) needs Viz to know a bit more about Skia's GrContext.

https://skia-review.googlesource.com/c/skia/+/198240 (Add GrRecordingContext variants of SkImage makeSubset, makeColorSpace and makeColorTypeAndColorSpace)

Change-Id: I5562adc1659e770a99d3abb0e4d045a44edfc782
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1509052Reviewed-by: weiliangc <weiliangc@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Cr-Commit-Position: refs/heads/master@{#638748}

components/viz/common/skia_helper.cc

@@ -6,6 +6,7 @@
 #include "cc/base/math_util.h"
 #include "third_party/skia/include/effects/SkOverdrawColorFilter.h"
 #include "third_party/skia/include/gpu/GrBackendSurface.h"
+#include "third_party/skia/include/gpu/GrContext.h"
 #include "ui/gfx/skia_util.h"
 
 namespace viz {