Align base::Pickle allocations to 4k boundaries

base/trace_event/trace_event_argument.cc

Index: base/trace_event/trace_event_argument.cc
diff --git a/base/trace_event/trace_event_argument.cc b/base/trace_event/trace_event_argument.cc
index 14a4499c1f6c52e0084b1c3cdfd7f1580d94337a..99bb32cc9d30a25ccf0091db0d00e6bffb4bdc6f 100644
--- a/base/trace_event/trace_event_argument.cc
+++ b/base/trace_event/trace_event_argument.cc
@@ -4,6 +4,7 @@
 
 #include "base/trace_event/trace_event_argument.h"
 
+#include "base/bits.h"
 #include "base/json/json_writer.h"
 #include "base/trace_event/trace_event_memory_overhead.h"
 #include "base/values.h"
@@ -453,9 +454,14 @@ void TracedValue::AppendAsTraceFormat(std::string* out) const {
 
 void TracedValue::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
+  const size_t kPickleAlignment = 4096;

[Lei Zhang, 2015/07/24 01:36:48]

Is this assuming |kPickleHeapAlign| in pickle.cc is 4096?

[Primiano Tucci (use gerrit), 2015/07/24 09:37:38]

Yes. It felt a bit of a stretch exposing it as a public const of base::Pickle as
it is an implementation detail and I find hard to think about other cases where
you need to know the heap size of Pickle. WDYT?
Should I move it to be Pickle::kPickleHeapAlign ?

I changed the name here (to match kPickleHeapAlign) and added a comment

[Lei Zhang, 2015/07/24 18:59:55]

Ok. Maybe expose it if we ever find another need to expose it.

   overhead->Add("TracedValue",
-                pickle_.GetTotalAllocatedSize() /* allocated size */,
-                pickle_.size() /* resident size */);
+
+                /* allocated size */
+                bits::Align(pickle_.GetTotalAllocatedSize(), kPickleAlignment),
+
+                /* resident size */
+                bits::Align(pickle_.size(), kPickleAlignment));
 }
 
 }  // namespace trace_event