Reduce space reserved for sandbox policy.

Metrics indicate that even outliers do not require more than two pages
(8k).  This change conservatively reduces the reserved size to six
pages.

A follow-on CL will remove the plumbing used to collect the metric.

Tests: existing sandbox and chrome tests.
Bug: 1059129
Change-Id: Id5c95cb5d3bf0e1b500732cf65927a7053d2856b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225256Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Alex Gough <ajgo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773900}

sandbox/win/src/ipc_leak_test.cc

@@ -46,7 +46,8 @@ enum TestId {
 
 // Helper function to allocate space (on the heap) for policy.
 PolicyGlobal* MakePolicyMemory() {
-  const size_t kTotalPolicySz = 4096 * 8;
+  // Should not exceed kPolMemSize from |sandbox_policy_base.cc|.
+  const size_t kTotalPolicySz = 4096 * 6;
   char* mem = new char[kTotalPolicySz];
   memset(mem, 0, kTotalPolicySz);
   PolicyGlobal* policy = reinterpret_cast<PolicyGlobal*>(mem);

sandbox/win/src/sandbox_policy_base.cc

@@ -44,7 +44,7 @@ namespace {
 constexpr size_t kOneMemPage = 4096;
 // The IPC and Policy shared memory sizes.
 constexpr size_t kIPCMemSize = kOneMemPage * 2;
-constexpr size_t kPolMemSize = kOneMemPage * 14;
+constexpr size_t kPolMemSize = kOneMemPage * 6;
 
 // Helper function to allocate space (on the heap) for policy.
 sandbox::PolicyGlobal* MakeBrokerPolicyMemory() {