Fix error handling in POSIX version of the base::File::GetLength.

chrome/browser/media/webrtc/webrtc_browsertest_audio.cc

Index: chrome/browser/media/webrtc/webrtc_browsertest_audio.cc
diff --git a/chrome/browser/media/webrtc/webrtc_browsertest_audio.cc b/chrome/browser/media/webrtc/webrtc_browsertest_audio.cc
index 3ed59478f354a22a1b6f7fbaa3d52c21cf3b7a2d..041cfa585b3a385946f74861618a78244b65361e 100644
--- a/chrome/browser/media/webrtc/webrtc_browsertest_audio.cc
+++ b/chrome/browser/media/webrtc/webrtc_browsertest_audio.cc
@@ -27,10 +27,23 @@ std::unique_ptr<char[]> ReadWavFile(const base::FilePath& wav_filename,
     return nullptr;
   }
 
-  size_t wav_file_length = wav_file.GetLength();
+  int64_t wav_file_length64 = wav_file.GetLength();
+  if (wav_file_length64 < 0) {
+    PLOG(ERROR) << "GetLength " << wav_file.GetPlatformFile();
+    return nullptr;
+  }
+  if (wav_file_length64 > std::numeric_limits<int>::max()) {
+    LOG(ERROR) << "File is too big: " << wav_filename.value();
+    return nullptr;
+  }
+  int wav_file_length = static_cast<int>(wav_file_length64);
+  if (!wav_file_length) {
+    LOG(ERROR) << "Input file is empty: " << wav_filename.value();
+    return nullptr;
+  }
 
   std::unique_ptr<char[]> data(new char[wav_file_length]);
-  size_t read_bytes = wav_file.Read(0, data.get(), wav_file_length);
+  int read_bytes = wav_file.Read(0, data.get(), wav_file_length);
   if (read_bytes != wav_file_length) {
     LOG(ERROR) << "Failed to read all bytes of " << wav_filename.value();
     return nullptr;