Add query for whether or not we have compressedTexSubImage

R=robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/430773004
diff --git a/src/gpu/GrDrawTargetCaps.h b/src/gpu/GrDrawTargetCaps.h
index b979b53..1a3a84c 100644
--- a/src/gpu/GrDrawTargetCaps.h
+++ b/src/gpu/GrDrawTargetCaps.h
@@ -40,6 +40,7 @@
     bool dstReadInShaderSupport() const { return fDstReadInShaderSupport; }
     bool discardRenderTargetSupport() const { return fDiscardRenderTargetSupport; }
     bool gpuTracingSupport() const { return fGpuTracingSupport; }
+    bool compressedTexSubImageSupport() const { return fCompressedTexSubImageSupport; }
 
     /**
      * Indicates whether GPU->CPU memory mapping for GPU resources such as vertex buffers and
@@ -90,6 +91,7 @@
     bool fDiscardRenderTargetSupport: 1;
     bool fReuseScratchTextures      : 1;
     bool fGpuTracingSupport         : 1;
+    bool fCompressedTexSubImageSupport : 1;
 
     uint32_t fMapBufferFlags;