Add detection of image load/store to caps

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4861

Change-Id: Ibf70cce9f61553e830b62339551c1541dc054e8b
Reviewed-on: https://skia-review.googlesource.com/4861
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/glsl/GrGLSLCaps.h b/src/gpu/glsl/GrGLSLCaps.h
index 137c9b7..4c53ad0 100644
--- a/src/gpu/glsl/GrGLSLCaps.h
+++ b/src/gpu/glsl/GrGLSLCaps.h
@@ -144,6 +144,11 @@
         return fSampleVariablesExtensionString;
     }
 
+    const char* imageLoadStoreExtensionString() const {
+        SkASSERT(this->imageLoadStoreSupport());
+        return fImageLoadStoreExtensionString;
+    }
+
     int maxVertexSamplers() const { return fMaxVertexSamplers; }
 
     int maxGeometrySamplers() const { return fMaxGeometrySamplers; }
@@ -152,6 +157,14 @@
 
     int maxCombinedSamplers() const { return fMaxCombinedSamplers; }
 
+    int maxVertexImages() const { return fMaxVertexImages; }
+
+    int maxGeometryImages() const { return fMaxGeometryImages; }
+
+    int maxFragmentImages() const { return fMaxFragmentImages; }
+
+    int maxCombinedImages() const { return fMaxCombinedImages; }
+
     /**
      * Given a texture's config, this determines what swizzle must be appended to accesses to the
      * texture in generated shader code. Swizzling may be implemented in texture parameters or a
@@ -215,6 +228,7 @@
     const char* fNoPerspectiveInterpolationExtensionString;
     const char* fMultisampleInterpolationExtensionString;
     const char* fSampleVariablesExtensionString;
+    const char* fImageLoadStoreExtensionString;
 
     const char* fFBFetchColorName;
     const char* fFBFetchExtensionString;
@@ -224,6 +238,11 @@
     int fMaxFragmentSamplers;
     int fMaxCombinedSamplers;
 
+    int fMaxVertexImages;
+    int fMaxGeometryImages;
+    int fMaxFragmentImages;
+    int fMaxCombinedImages;
+
     AdvBlendEqInteraction fAdvBlendEqInteraction;
 
     GrSwizzle fConfigTextureSwizzle[kGrPixelConfigCnt];