Implement basic stack traces on Android and reenable unit tests.

base/logging.cc

Index: base/logging.cc
diff --git a/base/logging.cc b/base/logging.cc
index 3b783871c33fbf913313382cda10441b7342f95f..16cd2f8b26d32f406e75b9c04c632674ce1ce708 100644
--- a/base/logging.cc
+++ b/base/logging.cc
@@ -556,9 +556,7 @@ LogMessage::LogMessage(const char* file, int line, LogSeverity severity,
 }
 
 LogMessage::~LogMessage() {
-  // TODO(port): enable stacktrace generation on LOG_FATAL once backtrace are
-  // working in Android.
-#if  !defined(NDEBUG) && !defined(OS_ANDROID) && !defined(OS_NACL)
+#if !defined(NDEBUG) && !defined(OS_NACL)
   if (severity_ == LOG_FATAL) {
     // Include a stack trace on a fatal.
     base::debug::StackTrace trace;