Add direct getter for GrCaps to GrContext.

TBR=joshualitt@google.com

Review URL: https://codereview.chromium.org/1149773005
diff --git a/src/gpu/GrAtlasTextContext.cpp b/src/gpu/GrAtlasTextContext.cpp
index 1d2cc4c..1006d4e 100644
--- a/src/gpu/GrAtlasTextContext.cpp
+++ b/src/gpu/GrAtlasTextContext.cpp
@@ -460,7 +460,7 @@
     // rasterizers and mask filters modify alpha, which doesn't
     // translate well to distance
     if (skPaint.getRasterizer() || skPaint.getMaskFilter() ||
-        !fContext->shaderDerivativeSupport()) {
+        !fContext->caps()->shaderCaps()->shaderDerivativeSupport()) {
         return false;
     }