Fix division by zero. Test filter with empty output.

net/filter/brotli_filter.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/filter/brotli_filter.h"
 
 #include "base/bit_cast.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/numerics/safe_conversions.h"
@@ skipping 23 matching lines @@
 
   ~BrotliFilter() override {
     BrotliDestroyState(brotli_state_);
     brotli_state_ = nullptr;
     DCHECK(used_memory_ == 0);
 
     UMA_HISTOGRAM_ENUMERATION(
         "BrotliFilter.Status", static_cast<int>(decoding_status_),
         static_cast<int>(DecodingStatus::DECODING_STATUS_COUNT));
     if (decoding_status_ == DecodingStatus::DECODING_DONE) {
-      UMA_HISTOGRAM_PERCENTAGE(
-          "BrotliFilter.CompressionPercent",
-          static_cast<int>((consumed_bytes_ * 100) / produced_bytes_));
+      // CompressionPercent is undefined when there is no output produced.
+      if (produced_bytes_ != 0) {
+        UMA_HISTOGRAM_PERCENTAGE(
+            "BrotliFilter.CompressionPercent",
+            static_cast<int>((consumed_bytes_ * 100) / produced_bytes_));
+      }
     }
 
     // All code here is for gathering stats, and can be removed when
     // BrotliFilter is considered stable.
     static const int kBuckets = 48;
     static const int64_t kMaxKb = 1 << (kBuckets / 3);  // 64MiB in KiB
     UMA_HISTOGRAM_CUSTOM_COUNTS("BrotliFilter.UsedMemoryKB",
                                 used_memory_maximum_ / 1024, 1, kMaxKb,
                                 kBuckets);
   }
@@ skipping 121 matching lines @@
   size_t produced_bytes_;
 
   DISALLOW_COPY_AND_ASSIGN(BrotliFilter);
 };
 
 Filter* CreateBrotliFilter(Filter::FilterType type_id) {
   return new BrotliFilter(type_id);
 }
 
 }  // namespace net