Move some of the logic from egl_cache_t into FileBlobCache

HWUI is using BlobCache to implement SkSL shader cache very
similar to egl_cache_t. Create a new class FileBlobCache,
that is used by both egl_cache_t and HWUI. FileBlobCache adds
the logic to save and load the BlobCache from a memory mapped
file.

Test: Built and ran Android. Verified that EGL cache still works
Test: for gmail and calc apps.
Bug: 66740665
Change-Id: Ia4d194963d039a60244f3bc76108844418adc99d
diff --git a/opengl/libs/EGL/FileBlobCache.h b/opengl/libs/EGL/FileBlobCache.h
new file mode 100644
index 0000000..393703f
--- /dev/null
+++ b/opengl/libs/EGL/FileBlobCache.h
@@ -0,0 +1,43 @@
+/*
+ ** Copyright 2017, The Android Open Source Project
+ **
+ ** Licensed under the Apache License, Version 2.0 (the "License");
+ ** you may not use this file except in compliance with the License.
+ ** You may obtain a copy of the License at
+ **
+ **     http://www.apache.org/licenses/LICENSE-2.0
+ **
+ ** Unless required by applicable law or agreed to in writing, software
+ ** distributed under the License is distributed on an "AS IS" BASIS,
+ ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ ** See the License for the specific language governing permissions and
+ ** limitations under the License.
+ */
+
+#ifndef ANDROID_FILE_BLOB_CACHE_H
+#define ANDROID_FILE_BLOB_CACHE_H
+
+#include "BlobCache.h"
+#include <string>
+
+namespace android {
+
+class FileBlobCache : public BlobCache {
+public:
+    // FileBlobCache attempts to load the saved cache contents from disk into
+    // BlobCache.
+    FileBlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize,
+            const std::string& filename);
+
+    // writeToFile attempts to save the current contents of BlobCache to
+    // disk.
+    void writeToFile();
+
+private:
+    // mFilename is the name of the file for storing cache contents.
+    std::string mFilename;
+};
+
+} // namespace android
+
+#endif // ANDROID_BLOB_CACHE_H