Image filters: de-nest SkImageFilter::Cache and Cache::Key.

src/core/SkImageFilterCache.h

Index: src/core/SkImageFilterCache.h
diff --git a/src/core/SkImageFilterCache.h b/src/core/SkImageFilterCache.h
new file mode 100644
index 0000000000000000000000000000000000000000..25079e194fc6b5d61ce05e64bf6ca6aba5ddc225
--- /dev/null
+++ b/src/core/SkImageFilterCache.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageFilterCache_DEFINED
+#define SkImageFilterCache_DEFINED
+
+#include "SkMatrix.h"
+#include "SkRefCnt.h"
+
+struct SkIPoint;
+class SkSpecialImage;
+
+struct SkImageFilterCacheKey {
+    SkImageFilterCacheKey(const uint32_t uniqueID, const SkMatrix& matrix,
+        const SkIRect& clipBounds, uint32_t srcGenID, const SkIRect& srcSubset)
+        : fUniqueID(uniqueID)
+        , fMatrix(matrix)
+        , fClipBounds(clipBounds)
+        , fSrcGenID(srcGenID)
+        , fSrcSubset(srcSubset) {
+        // Assert that Key is tightly-packed, since it is hashed.
+        static_assert(sizeof(SkImageFilterCacheKey) == sizeof(uint32_t) + sizeof(SkMatrix) +
+                                     sizeof(SkIRect) + sizeof(uint32_t) + 4 * sizeof(int32_t),
+                                     "image_filter_key_tight_packing");
+        fMatrix.getType();  // force initialization of type, so hashes match
+    }
+
+    uint32_t fUniqueID;
+    SkMatrix fMatrix;
+    SkIRect fClipBounds;
+    uint32_t fSrcGenID;
+    SkIRect fSrcSubset;
+
+    bool operator==(const SkImageFilterCacheKey& other) const {
+        return fUniqueID == other.fUniqueID &&
+               fMatrix == other.fMatrix &&
+               fClipBounds == other.fClipBounds &&
+               fSrcGenID == other.fSrcGenID &&
+               fSrcSubset == other.fSrcSubset;
+    }
+};
+
+// This cache maps from (filter's unique ID + CTM + clipBounds + src bitmap generation ID) to
+// (result, offset).
+class SkImageFilterCache : public SkRefCnt {
+public:
+    virtual ~SkImageFilterCache() {}
+    static SkImageFilterCache* Create(size_t maxBytes);
+    static SkImageFilterCache* Get();
+    virtual SkSpecialImage* get(const SkImageFilterCacheKey& key, SkIPoint* offset) const = 0;
+    virtual void set(const SkImageFilterCacheKey& key, SkSpecialImage* image,
+                     const SkIPoint& offset) = 0;
+    virtual void purge() = 0;
+    virtual void purgeByKeys(const SkImageFilterCacheKey[], int) = 0;
+    SkDEBUGCODE(virtual int count() const = 0;)
+};
+
+#endif