Add fake typed TRACE_EVENT macros for IOS and NACL builds.

This allows users to not care if tracing is supported on their system.

Bug: 916074
Change-Id: I69aa8178bb19f1a65186a2aba4f08699b6ba6ee3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1953210Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731514}

services/tracing/public/cpp/BUILD.gn

@@ -17,14 +17,42 @@ source_set("traced_process") {
 
   public_deps = [ "//services/tracing/public/mojom" ]
 
-  if (!is_nacl && !is_ios) {
-    deps = [ ":cpp" ]
-  }
+  deps = [ ":cpp" ]
 }
 
+# On IOS and NACL we don't support tracing so we only include the minimum needed
+# to support a fake typed TRACE_EVENT macro. However this means we don't have
+# any .cc files and thus on iOS and NaCl it needs to be a source_set and not a
+# component. |tracing_lib_type| decides which version to build.
 if (!is_nacl && !is_ios) {
-  component("cpp") {
-    sources = [
+  tracing_lib_type = "component"
+} else {
+  tracing_lib_type = "source_set"
+}
+
+target(tracing_lib_type, "cpp") {
+  sources = [
+    "perfetto/event_context.h",
+    "perfetto/macros.h",
+    "perfetto/macros_internal.h",
+  ]
+
+  defines = [ "IS_TRACING_CPP_IMPL" ]
+  output_name = "tracing_cpp"
+
+  configs += [ "//build/config/compiler:wexit_time_destructors" ]
+
+  public_deps = [
+    "//base",
+    "//third_party/perfetto:libperfetto",
+  ]
+
+  deps = [ "//third_party/perfetto/include/perfetto/protozero" ]
+
+  all_dependent_configs = [ "//third_party/perfetto/gn:public_config" ]
+
+  if (!is_nacl && !is_ios) {
+    sources += [
       "base_agent.cc",
       "base_agent.h",
       "perfetto/dummy_producer.cc",
@@ -40,9 +68,7 @@ if (!is_nacl && !is_ios) {
       "perfetto/java_heap_profiler/hprof_parser_android.h",
       "perfetto/java_heap_profiler/java_heap_profiler_android.cc",
       "perfetto/java_heap_profiler/java_heap_profiler_android.h",
-      "perfetto/macros.h",
       "perfetto/macros_internal.cc",
-      "perfetto/macros_internal.h",
       "perfetto/perfetto_config.cc",
       "perfetto/perfetto_config.h",
       "perfetto/perfetto_producer.cc",
@@ -79,24 +105,14 @@ if (!is_nacl && !is_ios) {
       "tracing_features.h",
     ]
 
-    defines = [ "IS_TRACING_CPP_IMPL" ]
-    output_name = "tracing_cpp"
-
-    configs += [ "//build/config/compiler:wexit_time_destructors" ]
-
-    public_deps = [
-      "//base",
+    public_deps += [
       "//components/tracing:startup_tracing",
       "//mojo/public/cpp/bindings",
       "//services/tracing/public/mojom",
-      "//third_party/perfetto:libperfetto",
     ]
 
-    all_dependent_configs = [ "//third_party/perfetto/gn:public_config" ]
-
-    deps = [
+    deps += [
       "//build:chromecast_buildflags",
-      "//third_party/perfetto/include/perfetto/protozero",
       "//third_party/perfetto/protos/perfetto/trace/chrome:minimal_complete_lite",
     ]
 
@@ -122,5 +138,5 @@ if (!is_nacl && !is_ios) {
       # stack_unwinder_android.cc overrides the dl_unwind_find_exidx function.
       all_dependent_configs += [ ":wrap_find_exidx" ]
     }
-  }
-}  # !is_nacl && !is_ios
+  }  # !is_ios && !is_nacl
+}

services/tracing/public/cpp/perfetto/macros.h

@@ -8,6 +8,11 @@
 #include "base/trace_event/trace_event.h"
 #include "services/tracing/public/cpp/perfetto/macros_internal.h"
 
+// Needed not for this file but for every user of the TRACE_EVENT macros for the
+// lambda definition. So included here for convenience.
+#include "services/tracing/public/cpp/perfetto/event_context.h"
+#include "third_party/perfetto/protos/perfetto/trace/track_event/track_event.pbzero.h"
+
 #if defined(TRACE_EVENT_BEGIN)
 #error "Another copy of perfetto tracing macros have been included"
 #endif

services/tracing/public/cpp/perfetto/macros_internal.h

@@ -5,14 +5,18 @@
 #ifndef SERVICES_TRACING_PUBLIC_CPP_PERFETTO_MACROS_INTERNAL_H_
 #define SERVICES_TRACING_PUBLIC_CPP_PERFETTO_MACROS_INTERNAL_H_
 
-#include "base/component_export.h"
-#include "base/trace_event/trace_event.h"
-#include "services/tracing/public/cpp/perfetto/trace_event_data_source.h"
+#include "build/build_config.h"
 
 namespace perfetto {
-class TrackEventContext;
+class EventContext;
 }
 
+#if !defined(OS_IOS) && !defined(OS_NACL)
+
+#include "base/component_export.h"
+#include "base/trace_event/trace_event.h"
+#include "services/tracing/public/cpp/perfetto/trace_event_data_source.h"
+
 namespace tracing {
 namespace internal {
 base::Optional<base::trace_event::TraceEvent> COMPONENT_EXPORT(TRACING_CPP)
@@ -24,7 +28,7 @@ base::Optional<base::trace_event::TraceEvent> COMPONENT_EXPORT(TRACING_CPP)
 // A simple function that will add the TraceEvent requested and will call the
 // |argument_func| after the track_event has been filled in.
 template <
-    typename TrackEventArgumentFunction = void (*)(perfetto::TrackEventContext)>
+    typename TrackEventArgumentFunction = void (*)(perfetto::EventContext)>
 static inline base::trace_event::TraceEventHandle AddTraceEvent(
     char phase,
     const unsigned char* category_group_enabled,
@@ -87,4 +91,33 @@ static inline base::trace_event::TraceEventHandle AddTraceEvent(
     return 0;                                                                 \
   }()};
 
+#else  // !defined(OS_IOS) && !defined(OS_NACL)
+
+// Tracing isn't supported on IOS or NACL so we just black hole all the
+// parameters into a function that doesn't do anything. This ensures that no
+// warnings about unused parameters are generated.
+
+namespace tracing {
+namespace internal {
+template <
+    typename TrackEventArgumentFunction = void (*)(perfetto::EventContext)>
+static inline base::trace_event::TraceEventHandle AddTraceEvent(
+    char,
+    const unsigned char*,
+    const char*,
+    unsigned int,
+    TrackEventArgumentFunction) {
+  return {0, 0, 0};
+}
+}  // namespace internal
+}  // namespace tracing
+
+#define TRACING_INTERNAL_ADD_TRACE_EVENT(phase, category, name, flags, ...) \
+  tracing::internal::AddTraceEvent(phase, nullptr, name, flags, ##__VA_ARGS__);
+
+#define TRACING_INTERNAL_SCOPED_ADD_TRACE_EVENT(category, name, ...)           \
+  TRACING_INTERNAL_ADD_TRACE_EVENT('B', category, name, TRACE_EVENT_FLAG_NONE, \
+                                   ##__VA_ARGS__);
+#endif  // else of !defined(OS_IOS) && !defined(OS_NACL)
+
 #endif  // SERVICES_TRACING_PUBLIC_CPP_PERFETTO_MACROS_INTERNAL_H_