base: Add crash keys

This CL adds support for crash keys (named after
chromium's CrashKey). A Crash Key is a global
variable, which can be either cleared, set to an
integer value or a string value.
When a crash report is generated, the non-cleared
crash keys are appended to the crash log.

Test: perfetto_unittests --gtest_filter=CrashKeysTest.*
Bug: 202283508
Change-Id: I4b374d22a97659bb9598c01e3e88fa4bb88bb59f
diff --git a/Android.bp b/Android.bp
index 3b4bbdd..563cfa8 100644
--- a/Android.bp
+++ b/Android.bp
@@ -6838,6 +6838,7 @@
 filegroup {
     name: "perfetto_src_base_base",
     srcs: [
+        "src/base/crash_keys.cc",
         "src/base/ctrl_c_handler.cc",
         "src/base/event_fd.cc",
         "src/base/file_utils.cc",