Add a field trial for using lower sqlite cache sizes.

chrome/browser/history/history_database.cc

Index: chrome/browser/history/history_database.cc
===================================================================
--- chrome/browser/history/history_database.cc	(revision 106923)
+++ chrome/browser/history/history_database.cc	(working copy)
@@ -14,6 +14,7 @@
 #include "base/rand_util.h"
 #include "base/string_util.h"
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
+#include "chrome/browser/history/history_field_trial.h"
 #include "sql/transaction.h"
 
 #if defined(OS_MACOSX)
@@ -78,11 +79,15 @@
   // this is a NOP. Must be a power of 2 and a max of 8192.
   db_.set_page_size(4096);
 
-  // Increase the cache size. The page size, plus a little extra, times this
-  // value, tells us how much memory the cache will use maximum.
-  // 6000 * 4MB = 24MB
-  // TODO(brettw) scale this value to the amount of available memory.
-  db_.set_cache_size(6000);
+  if (HistoryFieldTrial::IsLowMemFieldTrial()) {
+    db_.set_cache_size(500);
+  } else {
+    // Increase the cache size. The page size, plus a little extra, times this
+    // value, tells us how much memory the cache will use maximum.
+    // 6000 * 4MB = 24MB
+    // TODO(brettw) scale this value to the amount of available memory.
+    db_.set_cache_size(6000);
+  }
 
   // Note that we don't set exclusive locking here. That's done by
   // BeginExclusiveMode below which is called later (we have to be in shared