Introduce microdump writer class.

Microdumps are a very lightweight variant of minidumps. They are meant
to dump a minimal crash report on the system log (logcat on Android),
containing only the state of the crashing thread.
This is to deal with cases where the user has opted out from crash
uploading but we still want to generate meaningful information on the
device to pull a stacktrace for development purposes.
Conversely to conventional stack traces (e.g. the one generated by
Android's debuggerd or Chromium's base::stacktrace) microdumps do NOT
require unwind tables to be present in the target binary. This allows
to save precious binary size (~1.5 MB for Chrome on Arm, ~10 MB on
arm64).
More information and design doc on crbug.com/410294

BUG=chromium:410294

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1398 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/client/linux/handler/exception_handler.cc

@@ -91,6 +91,7 @@
 #include "common/linux/linux_libc_support.h"
 #include "common/memory.h"
 #include "client/linux/log/log.h"
+#include "client/linux/microdump_writer/microdump_writer.h"
 #include "client/linux/minidump_writer/linux_dumper.h"
 #include "client/linux/minidump_writer/minidump_writer.h"
 #include "common/linux/eintr_wrapper.h"
@@ -210,7 +211,8 @@ ExceptionHandler::ExceptionHandler(const MinidumpDescriptor& descriptor,
   if (server_fd >= 0)
     crash_generation_client_.reset(CrashGenerationClient::TryCreate(server_fd));
 
-  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD())
+  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD() &&
+      !minidump_descriptor_.IsMicrodumpOnConsole())
     minidump_descriptor_.UpdatePath();
 
   pthread_mutex_lock(&g_handler_stack_mutex_);
@@ -548,6 +550,12 @@ void ExceptionHandler::WaitForContinueSignal() {
 // Runs on the cloned process.
 bool ExceptionHandler::DoDump(pid_t crashing_process, const void* context,
                               size_t context_size) {
+  if (minidump_descriptor_.IsMicrodumpOnConsole()) {
+    return google_breakpad::WriteMicrodump(crashing_process,
+                                           context,
+                                           context_size,
+                                           mapping_list_);
+  }
   if (minidump_descriptor_.IsFD()) {
     return google_breakpad::WriteMinidump(minidump_descriptor_.fd(),
                                           minidump_descriptor_.size_limit(),
@@ -583,7 +591,8 @@ bool ExceptionHandler::WriteMinidump(const string& dump_path,
 __attribute__((optimize("no-omit-frame-pointer")))
 #endif
 bool ExceptionHandler::WriteMinidump() {
-  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD()) {
+  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD() &&
+      !minidump_descriptor_.IsMicrodumpOnConsole()) {
     // Update the path of the minidump so that this can be called multiple times
     // and new files are created for each minidump.  This is done before the
     // generation happens, as clients may want to access the MinidumpDescriptor