Explicitly compare to NULL when looking for weak_import symbols.

base/debug_util_posix.cc

 // Copyright (c) 2006-2009 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 "build/build_config.h"
 #include "base/debug_util.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
@@ skipping 103 matching lines @@
 void DebugUtil::BreakDebugger() {
 #if defined(ARCH_CPU_ARM_FAMILY)
   asm("bkpt 0");
 #else
   asm("int3");
 #endif
 }
 
 StackTrace::StackTrace() {
 #if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_5
-  if (!backtrace) {
+  if (backtrace == NULL) {
     count_ = 0;
     return;
   }
 #endif
   // Though the backtrace API man page does not list any possible negative
   // return values, we take no chance.
   count_ = std::max(backtrace(trace_, arraysize(trace_)), 0);
 }
 
 void StackTrace::PrintBacktrace() {
 #if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_5
-  if (!backtrace_symbols_fd)
+  if (backtrace_symbols_fd == NULL)
     return;
 #endif
   fflush(stderr);
   backtrace_symbols_fd(trace_, count_, STDERR_FILENO);
 }
 
 void StackTrace::OutputToStream(std::ostream* os) {
 #if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_5
-  if (!backtrace_symbols)
+  if (backtrace_symbols == NULL)
     return;
 #endif
   scoped_ptr_malloc<char*> trace_symbols(backtrace_symbols(trace_, count_));
 
   // If we can't retrieve the symbols, print an error and just dump the raw
   // addresses.
   if (trace_symbols.get() == NULL) {
     (*os) << "Unable get symbols for backtrace (" << strerror(errno)
           << "). Dumping raw addresses in trace:\n";
     for (int i = 0; i < count_; ++i) {
       (*os) << "\t" << trace_[i] << "\n";
     }
   } else {
     (*os) << "Backtrace:\n";
     for (int i = 0; i < count_; ++i) {
       (*os) << "\t" << trace_symbols.get()[i] << "\n";
     }
   }
 }