Add a field trial for using lower sqlite cache sizes.

chrome/browser/history/text_database.cc

Index: chrome/browser/history/text_database.cc
===================================================================
--- chrome/browser/history/text_database.cc	(revision 106923)
+++ chrome/browser/history/text_database.cc	(working copy)
@@ -15,6 +15,7 @@
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
+#include "chrome/browser/history/history_field_trial.h"
 #include "sql/statement.h"
 #include "sql/transaction.h"
 
@@ -138,7 +139,13 @@
   // have 2-3 of these objects, each with their own 8MB, this adds up very fast.
   // We therefore reduce the size so when there are multiple objects, we're not
   // too big.
-  db_.set_cache_size(512);
+  if (HistoryFieldTrial::IsLowMemFieldTrial()) {
+    // FTS does merges of 16 pages at a time, so we need a working set size
+    // somewhat greater than that to prevent too much thrashing.
+    db_.set_cache_size(128);
+  } else {
+    db_.set_cache_size(512);
+  }
 
   // Run the database in exclusive mode. Nobody else should be accessing the
   // database while we're running, and this will give somewhat improved perf.