Fix size_t/int comparison/conversion issues in leveldb.

The create function took |num_keys| as an int, but callers and implementers wanted it to function as a size_t (e.g. passing std::vector::size() in, passing it to vector constructors as a size arg, indexing containers by it, etc.).  This resulted in implicit conversions between the two types as well as warnings (found with Chromium's external copy of these sources, built with MSVC) about signed vs. unsigned comparisons.

The leveldb sources were already widely using size_t elsewhere, e.g. for key and filter lengths, so using size_t here is not inconsistent with the existing code.  However, it does change the public C API.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=101074871

table/filter_block.cc

@@ -68,7 +68,7 @@ void FilterBlockBuilder::GenerateFilter() {
 
   // Generate filter for current set of keys and append to result_.
   filter_offsets_.push_back(result_.size());
-  policy_->CreateFilter(&tmp_keys_[0], num_keys, &result_);
+  policy_->CreateFilter(&tmp_keys_[0], static_cast<int>(num_keys), &result_);
 
   tmp_keys_.clear();
   keys_.clear();
@@ -97,7 +97,7 @@ bool FilterBlockReader::KeyMayMatch(uint64_t block_offset, const Slice& key) {
   if (index < num_) {
     uint32_t start = DecodeFixed32(offset_ + index*4);
     uint32_t limit = DecodeFixed32(offset_ + index*4 + 4);
-    if (start <= limit && limit <= (offset_ - data_)) {
+    if (start <= limit && limit <= static_cast<size_t>(offset_ - data_)) {
       Slice filter = Slice(data_ + start, limit - start);
       return policy_->KeyMayMatch(key, filter);
     } else if (start == limit) {

util/bloom.cc

@@ -47,7 +47,7 @@ class BloomFilterPolicy : public FilterPolicy {
     dst->resize(init_size + bytes, 0);
     dst->push_back(static_cast<char>(k_));  // Remember # of probes in filter
     char* array = &(*dst)[init_size];
-    for (size_t i = 0; i < n; i++) {
+    for (int i = 0; i < n; i++) {
       // Use double-hashing to generate a sequence of hash values.
       // See analysis in [Kirsch,Mitzenmacher 2006].
       uint32_t h = BloomHash(keys[i]);

util/bloom_test.cc

@@ -46,7 +46,8 @@ class BloomTest {
       key_slices.push_back(Slice(keys_[i]));
     }
     filter_.clear();
-    policy_->CreateFilter(&key_slices[0], key_slices.size(), &filter_);
+    policy_->CreateFilter(&key_slices[0], static_cast<int>(key_slices.size()),
+                          &filter_);
     keys_.clear();
     if (kVerbose >= 2) DumpFilter();
   }