[tracing] Introduce "allowed_dump_modes" for memory dump config

content/browser/tracing/background_tracing_manager_impl.cc

Index: content/browser/tracing/background_tracing_manager_impl.cc
diff --git a/content/browser/tracing/background_tracing_manager_impl.cc b/content/browser/tracing/background_tracing_manager_impl.cc
index 13c60a93e12d62d95d69962d7f97efdf5cccc696..14746163c2cd28098ffb8de72a0e58835f278103 100644
--- a/content/browser/tracing/background_tracing_manager_impl.cc
+++ b/content/browser/tracing/background_tracing_manager_impl.cc
@@ -50,10 +50,13 @@ void RecordBackgroundTracingMetric(BackgroundTracingMetrics metric) {
 }
 
 // Tracing enabled callback for BENCHMARK_MEMORY_LIGHT category preset.
-// TODO(ssid): Remove this when background tracing supports trace config strings
-// and memory-infra supports peak detection crbug.com/609935.
 void BenchmarkMemoryLight_TracingEnabledCallback() {
-  base::trace_event::MemoryDumpManager::GetInstance()->RequestGlobalDump(
+  auto dump_manager = base::trace_event::MemoryDumpManager::GetInstance();
+  // Safety check to make sure the memory-infra restrictions are properly

[oystein (OOO til 10th of July), 2016/06/20 17:02:18]

I'm a bit confused by this. Why does it matter whether or not the detailed LOD
is allowed, at this point? 

[ssid, 2016/06/20 19:12:06]

So, this is here to ensure that all this code in this CL is working.
Suppose there was a mistake and the trace config did not get propagated to
renderer process or the correct trace config wasn't given background controller
and a heavy dump could be triggered then we might end up uploading sensitive
data.
So, this check would crash here instead of uploading the data.

[Primiano Tucci (use gerrit), 2016/06/21 06:50:49]

Yup this is essentially my paranoy in action. It's quite easy to screw up the
trace config plumbing, and this is a final cross-check to make chrome suicide if
we do that (at least with memory-infra stuff).
I prefer getting bugs assigned for crashes than having to write privacy screwup
postmortems :)

+  // propagated via TraceConfig
+  CHECK(!dump_manager->IsDumpModeAllowed(
+      base::trace_event::MemoryDumpLevelOfDetail::DETAILED));
+  dump_manager->RequestGlobalDump(
       base::trace_event::MemoryDumpType::EXPLICITLY_TRIGGERED,
       base::trace_event::MemoryDumpLevelOfDetail::BACKGROUND);
 }
@@ -414,8 +417,13 @@ void BackgroundTracingManagerImpl::StartTracing(
                            BENCHMARK_MEMORY_LIGHT) {
     // On memory light mode, the periodic memory dumps are disabled and a single
     // memory dump is requested after tracing is enabled in all the processes.
-    trace_config.ResetMemoryDumpConfig(
-        base::trace_event::TraceConfig::MemoryDumpConfig());
+    // TODO(ssid): Remove this when background tracing supports trace config
+    // strings and memory-infra supports peak detection crbug.com/609935.
+    base::trace_event::TraceConfig::MemoryDumpConfig memory_config;
+    memory_config.allowed_dump_modes =
+        std::set<base::trace_event::MemoryDumpLevelOfDetail>(
+            {base::trace_event::MemoryDumpLevelOfDetail::BACKGROUND});
+    trace_config.ResetMemoryDumpConfig(memory_config);
     tracing_enabled_callback =
         base::Bind(&BenchmarkMemoryLight_TracingEnabledCallback);
   }