[not part of build] create the cache directory if it doesn't exist already.

netwerk/cache/src/nsDiskCacheDevice.cpp

@@ -86,6 +86,7 @@ static nsresult installPrefListeners(nsDiskCacheDevice* device)
         rv = cacheDirectory->Append("Cache");
     	if (NS_FAILED(rv))
     		return rv;
+
         rv = prefs->SetFileXPref(CACHE_DIR_PREF, cacheDirectory);
     	if (NS_FAILED(rv))
     		return rv;
@@ -93,6 +94,11 @@ static nsresult installPrefListeners(nsDiskCacheDevice* device)
         return rv;
 #endif
     } else {
+        // be a good citizen in the current Cache directory.
+        rv = cacheDirectory->Append("NewCache");
+        if (NS_FAILED(rv))
+            return rv;
+    
         // cause the preference to be set up initially.
         device->setCacheDirectory(cacheDirectory);
     }
@@ -344,6 +350,12 @@ nsDiskCacheDevice::OnDataSizeChange(nsCacheEntry * entry, PRInt32 deltaSize)
 void nsDiskCacheDevice::setCacheDirectory(nsILocalFile* cacheDirectory)
 {
     mCacheDirectory = cacheDirectory;
+
+    // make sure the Cache directory exists.
+    PRBool exists;
+    nsresult rv = cacheDirectory->Exists(&exists);
+    if (NS_SUCCEEDED(rv) && !exists)
+        cacheDirectory->Create(nsIFile::DIRECTORY_TYPE, 0777);
 }
 
 nsresult nsDiskCacheDevice::getFileForKey(const char* key, PRBool meta, nsIFile ** result)