Make the benchmark timeout a floating point, not integer, flag.

Allows running benchmarks at very low times like 0.02 seconds.

Useful for making graphs like
https://screenshot.googleplex.com/87RUcHaF7Sqmwij (internal) where exact
values aren't super important but quick results are nice.

Change-Id: Ia45f0299b392c5cae4258c88cd9ae2f2cc63070f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/85067
Auto-Submit: Rudolf Polzer <rpolzer@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

tool/speed.cc

diff --git a/tool/speed.cc b/tool/speed.cc
index ddbfa85..1a6f3c7 100644
--- a/tool/speed.cc
+++ b/tool/speed.cc
@@ -191,7 +191,7 @@
 
 uint64_t (*time_now)() = time_now_realtime;
 
-static uint64_t g_timeout_seconds = 1;
+static double g_timeout_seconds = 1;
 static std::vector<size_t> g_chunk_lengths = {16, 256, 1350, 8192, 16384};
 
 // IterationsBetweenTimeChecks returns the number of iterations of |func| to run
@@ -1905,7 +1905,7 @@
   }
 
   if (args_map.count("-timeout") != 0) {
-    g_timeout_seconds = atoi(args_map["-timeout"].c_str());
+    g_timeout_seconds = atof(args_map["-timeout"].c_str());
   }
 
 #if defined(OPENSSL_TIME_NOW_CPUTIME)