Create image cache for use by json canvas

tools/UrlDataManager.h

+/*
+ * 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 SkUrlDataManager_DEFINED
+#define SkUrlDataManager_DEFINED
+
+#include "SkChecksum.h"
+#include "SkData.h"
+#include "SkString.h"
+#include "SkTDynamicHash.h"
+
+/*
+ * A simple class which allows clients to add opaque data types, and returns a url where this data
+ * will be hosted.  Its up to the owner of this class to actually serve the data.
+ */
+bool operator==(const SkData& a, const SkData& b);
+
+class UrlDataManager {
+public:
+    UrlDataManager(SkString rootUrl);
+    ~UrlDataManager() { this->reset(); }
+
+    SkString addData(SkData*, const char* contentType);

[ethannicholas, 2016/02/08 14:26:35]

Can we get some documentation on this method, e.g. clarify that calling it twice
with two identical SkDatas results in the same URL?

+
+    struct UrlData : public SkRefCnt {
+        SkString fUrl;
+        SkString fContentType;
+        SkAutoTUnref<SkData> fData;
+    };
+
+    UrlData* getDataFromUrl(SkString url) {
+        return fUrlLookup.find(url);
+    }
+    void reset();
+
+private:
+    struct LookupTrait {
+        // We use the data as a hash, this is not really optimal but is fine until proven otherwise
+        static const SkData& GetKey(const UrlData& data) {
+            return *data.fData.get();
+        }
+
+        static uint32_t Hash(const SkData& key) {
+            return SkChecksum::Murmur3(key.bytes(), key.size());
+        }
+    };
+
+    struct ReverseLookupTrait {
+        static const SkString& GetKey(const UrlData& data) {
+            return data.fUrl;
+        }
+
+        static uint32_t Hash(const SkString& key) {
+            return SkChecksum::Murmur3(key.c_str(), strlen(key.c_str()));
+        }
+    };
+
+
+    SkString fRootUrl;
+    SkTDynamicHash<UrlData, SkData, LookupTrait> fCache;
+    SkTDynamicHash<UrlData, SkString, ReverseLookupTrait> fUrlLookup;
+    uint32_t fDataId;
+};
+
+#endif