Use '/protos/' as import prefix of perfetto protos

Historically we referred to our protos assuming
./protos as the source path. So all protos did
import "perfetto/trace/xxx.proto" and C++ code did
#include "perfetto/trace/xxx.pb(zero).h".
This CL makes everything relative to the repo root,
so now things look like
import "protos/perfetto/trace/xxx.proto", likewise
for #includes.
A lot of tooling out there (mainly bazel) seems to
assume that protos are referred to relatively from
the project root. Dealing with the current situation
seems prohibitively complex.

Bug: 140126865
Change-Id: I391aafaf276b68d3576ee16157dba0155dcb0879
diff --git a/src/tracing/core/test_config.cc b/src/tracing/core/test_config.cc
index 78b692b..decebf7 100644
--- a/src/tracing/core/test_config.cc
+++ b/src/tracing/core/test_config.cc
@@ -18,7 +18,7 @@
  * AUTOGENERATED - DO NOT EDIT
  *******************************************************************************
  * This file has been generated from the protobuf message
- * perfetto/config/test_config.proto
+ * protos/perfetto/config/test_config.proto
  * by
  * ../../tools/proto_to_cpp/proto_to_cpp.cc.
  * If you need to make changes here, change the .proto file and then run
@@ -27,7 +27,7 @@
 
 #include "perfetto/tracing/core/test_config.h"
 
-#include "perfetto/config/test_config.pb.h"
+#include "protos/perfetto/config/test_config.pb.h"
 
 namespace perfetto {