Convert GrMesh to a struct

Converts GrMesh to a struct and changes the names/semantics of its
fields to be more inline with their GL counterparts. Also renames the
"instancing" feature to "pattern", to avoid ambiguity with hardware
instancing.

Bug: skia:
Change-Id: Ia0999d4f9c83b5dd31f81b9bf4f36ed9abd26286
Reviewed-on: https://skia-review.googlesource.com/15157
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/ops/GrAAFillRectOp.cpp b/src/gpu/ops/GrAAFillRectOp.cpp
index 7bf62ec..ca91e94 100644
--- a/src/gpu/ops/GrAAFillRectOp.cpp
+++ b/src/gpu/ops/GrAAFillRectOp.cpp
@@ -41,7 +41,7 @@
     // clang-format on
 
     GR_STATIC_ASSERT(SK_ARRAY_COUNT(gFillAARectIdx) == kIndicesPerAAFillRect);
-    return resourceProvider->findOrCreateInstancedIndexBuffer(
+    return resourceProvider->findOrCreatePatternedIndexBuffer(
             gFillAARectIdx, kIndicesPerAAFillRect, kNumAAFillRectsInIndexBuffer,
             kVertsPerAAFillRect, gAAFillRectIndexBufferKey);
 }
@@ -231,7 +231,7 @@
         size_t vertexStride = gp->getVertexStride();
 
         sk_sp<const GrBuffer> indexBuffer(get_index_buffer(target->resourceProvider()));
-        InstancedHelper helper;
+        PatternHelper helper;
         void* vertices =
                 helper.init(target, kTriangles_GrPrimitiveType, vertexStride, indexBuffer.get(),
                             kVertsPerAAFillRect, kIndicesPerAAFillRect, fRectCnt);