Configure the Widevine cache buffer size via a property

The property ro.com.widevine.cachesize may be set on a device to override the
default stream buffer cache size.

related-to-bug: 6819880

Change-Id: I27da154e38289c5d1f5f2f5f424202253d0721cc

proprietary/wvm/include/WVMExtractorImpl.h

@@ -80,7 +80,9 @@ private:
 
     status_t readMetaData();
 
-    const static size_t kStreamCacheSize = 10 * 1024 * 1024;
+    size_t getStreamCacheSize() const;
+
+    const static size_t kDefaultStreamCacheSize = 10 * 1024 * 1024;
 
     WVMExtractorImpl(const WVMExtractorImpl &);
     WVMExtractorImpl &operator=(const WVMExtractorImpl &);