Add 1st cut of FileSystemUsageTracker that tracks the usage changes in FileSystem API.

webkit/fileapi/sandboxed_file_system_context.cc

Index: webkit/fileapi/sandboxed_file_system_context.cc
diff --git a/webkit/fileapi/sandboxed_file_system_context.cc b/webkit/fileapi/sandboxed_file_system_context.cc
index 16232d5d35cdf70f0c313f6237c50326f6a7874a..6141f74ad1bd2fc3305f0fb0f0b509af0909b8ce 100644
--- a/webkit/fileapi/sandboxed_file_system_context.cc
+++ b/webkit/fileapi/sandboxed_file_system_context.cc
@@ -8,6 +8,7 @@
 #include "base/message_loop_proxy.h"
 #include "webkit/fileapi/file_system_path_manager.h"
 #include "webkit/fileapi/file_system_quota_manager.h"
+#include "webkit/fileapi/file_system_usage_tracker.h"
 
 namespace fileapi {
 
@@ -23,7 +24,9 @@ SandboxedFileSystemContext::SandboxedFileSystemContext(
       path_manager_(new FileSystemPathManager(
           file_message_loop, profile_path, is_incognito, allow_file_access)),
       quota_manager_(new FileSystemQuotaManager(
-          allow_file_access, unlimited_quota)) {
+          allow_file_access, unlimited_quota)),
+      usage_tracker_(new FileSystemUsageTracker(
+          file_message_loop, profile_path, is_incognito)) {
 }
 
 SandboxedFileSystemContext::~SandboxedFileSystemContext() {