[DiskCache] Disable HTTP disk cache if not enouhg disk space

Hidden behind WPE_DISK_CACHE_SIZE env

There is no control over available disk space for HTTP network cache.
Entries are written to disk asynchronously (using file memory mapping)
so lack of disk space results with SIGBUS signal and WPENetworkProcess crash.

Author: asurdej-comcast

Source/WebKit/Shared/CacheModel.cpp

@@ -27,6 +27,7 @@
 #include "CacheModel.h"
 
 #include <algorithm>
+#include <wtf/Assertions.h>
 #include <wtf/RAMSize.h>
 #include <wtf/Seconds.h>
 #include <wtf/StdLibExtras.h>
@@ -183,8 +184,12 @@ uint64_t calculateURLCacheDiskCapacity(CacheModel cacheModel, uint64_t diskFreeS
         if (units != 1)
             value = value.substring(0, value.length()-1);
 
-        size_t size = size_t(parseInteger<uint64_t>(value).value_or(0) * units);
-        urlCacheDiskCapacity = (unsigned long)(size);
+        urlCacheDiskCapacity = parseInteger<uint64_t>(value).value_or(0) * units;
+        if (urlCacheDiskCapacity > diskFreeSize * MB) {
+            WTFLogAlways("Disabling cache due to lack of disk space (wanted space: %ju, disk free space: %ju [bytes])",
+                         urlCacheDiskCapacity, diskFreeSize * MB);
+            urlCacheDiskCapacity = 0;
+        }
     }
 
     return urlCacheDiskCapacity;