Fix 'ordered comparison between pointer and zero' errors

media/audio/win/audio_output_win_unittest.cc

 // Copyright (c) 2012 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 <windows.h>
 #include <mmsystem.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 120 matching lines @@
     ::VirtualQuery(start_, &mbi, sizeof(mbi));
     size_ = mbi.RegionSize;
   }
   ~ReadOnlyMappedFile() {
     if (start_) {
       ::UnmapViewOfFile(start_);
       ::CloseHandle(fmap_);
     }
   }
   // Returns true if the file was successfully mapped.
-  bool is_valid() const {
-    return ((start_ > 0) && (size_ > 0));
-  }
+  bool is_valid() const { return (start_ && (size_ > 0)); }
   // Returns the size in bytes of the mapped memory.
   uint32_t size() const { return size_; }
   // Returns the memory backing the file.
   const void* GetChunkAt(uint32_t offset) { return &start_[offset]; }
 
  private:
   HANDLE fmap_;
   char* start_;
   uint32_t size_;
 };
@@ skipping 498 matching lines @@
   oas->Start(&source);
 
   ::WaitForSingleObject(thread, INFINITE);
   ::CloseHandle(thread);
 
   oas->Stop();
   oas->Close();
 }
 
 }  // namespace media