sql: Make //sql/vfs_wrapper.cc compatible with SQLITE_OMIT_DEPRECATED.

Our SQLite VFS [1] wrapper implementation unconditionally wraps
xCurrentTime(). However, when SQLite is compiled with the
SQLITE_OMIT_DEPRECATED option [2], xCurrentTime() is null for the VFS
implementations that ship with SQLite, because xCurrentTime() was
deprecated in favor of xCurrentTimeInt64().

This CL replaces the unconditional wrapper with a conditional wrapper.
This ensures that our VFS wrapper exposes an xCurrentTimeInt64()
implementation when used with a modern SQLite library (like the one
bundled with Chromium), and an xCurrentTime() implementation when using
an older SQLite version (which might be the case when using the library
bundled with the operating system).

[1] https://www.sqlite.org/c3ref/vfs.html
[2] https://www.sqlite.org/compile.html#omit_deprecated

Bug: 807093
Change-Id: Id26cc4517a1a23692e7860ed620348c027db990f
Reviewed-on: https://chromium-review.googlesource.com/892484Reviewed-by: Chris Mumford <cmumford@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532969}

sql/vfs_wrapper.cc

@@ -498,7 +498,9 @@ sqlite3_vfs* VFSWrapper() {
   wrapper_vfs->xDlClose = &DlClose;
   wrapper_vfs->xRandomness = &Randomness;
   wrapper_vfs->xSleep = &Sleep;
-  wrapper_vfs->xCurrentTime = &CurrentTime;
+  // |xCurrentTime| is null when SQLite is built with SQLITE_OMIT_DEPRECATED.
+  wrapper_vfs->xCurrentTime =
+      (wrapped_vfs->xCurrentTime ? &CurrentTime : nullptr);
   wrapper_vfs->xGetLastError = &GetLastError;
   // The methods above are in version 1 of sqlite_vfs.
   // There were VFS implementations with nullptr for |xCurrentTimeInt64|.