Fix uninitialized read in the SimpleCache tests.

net/disk_cache/entry_unittest.cc

Index: net/disk_cache/entry_unittest.cc
diff --git a/net/disk_cache/entry_unittest.cc b/net/disk_cache/entry_unittest.cc
index 4a2cf67c362eba989a94c7dc577b0241f93b7d99..659e49f511d2faba6860720d681108805d300c2e 100644
--- a/net/disk_cache/entry_unittest.cc
+++ b/net/disk_cache/entry_unittest.cc
@@ -2853,6 +2853,7 @@ TEST_F(DiskCacheEntryTest, SimpleCacheOptimisticWriteReleases) {
   const int kWriteSize = 512;
   scoped_refptr<net::IOBuffer> buffer1(new net::IOBuffer(kWriteSize));
   EXPECT_TRUE(buffer1->HasOneRef());
+  CacheTestFillBuffer(buffer1->data(), kWriteSize, false);
 
   // An optimistic write happens only when there is an empty queue of pending
   // operations. To ensure the queue is empty, we issue a write and wait until