Reserve space before building potentially large vectors in safe-browsing.

In cases where we can approximate the vector size in advance,
reserve() that much space rather than building organically.

BUG=97102
TEST=Reduction in crash rate for that bug.


Review URL: http://codereview.chromium.org/8005001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@102435 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/safe_browsing/prefix_set.cc

@@ -42,6 +42,13 @@ namespace safe_browsing {
 PrefixSet::PrefixSet(const std::vector<SBPrefix>& sorted_prefixes)
     : checksum_(0) {
   if (sorted_prefixes.size()) {
+    // Estimate the resulting vector sizes.  There will be strictly
+    // more than |min_runs| entries in |index_|, but there generally
+    // aren't many forced breaks.
+    const size_t min_runs = sorted_prefixes.size() / kMaxRun;
+    index_.reserve(min_runs);
+    deltas_.reserve(sorted_prefixes.size() - min_runs);
+
     // Lead with the first prefix.
     SBPrefix prev_prefix = sorted_prefixes[0];
     size_t run_length = 0;
@@ -141,6 +148,8 @@ bool PrefixSet::Exists(SBPrefix prefix) const {
 }
 
 void PrefixSet::GetPrefixes(std::vector<SBPrefix>* prefixes) const {
+  prefixes->reserve(index_.size() + deltas_.size());
+
   for (size_t ii = 0; ii < index_.size(); ++ii) {
     // The deltas for this |index_| entry run to the next index entry,
     // or the end of the deltas.

chrome/browser/safe_browsing/safe_browsing_database.cc

@@ -269,6 +269,7 @@ safe_browsing::PrefixSet* PrefixSetFromAddPrefixes(
   // |prefixes|.  For now, |prefixes| is useful while debugging
   // things.
   std::vector<SBPrefix> prefixes;
+  prefixes.reserve(add_prefixes.size());
   for (size_t i = 0; i < add_prefixes.size(); ++i) {
     prefixes.push_back(add_prefixes[i].prefix);
   }
@@ -1406,6 +1407,7 @@ void SafeBrowsingDatabaseNew::LoadWhitelist(
   }
 
   std::vector<SBFullHash> new_whitelist;
+  new_whitelist.reserve(full_hashes.size());
   for (std::vector<SBAddFullHash>::const_iterator it = full_hashes.begin();
        it != full_hashes.end(); ++it) {
     new_whitelist.push_back(it->full_hash);