Fix incorrect computation of size exported to JSON traces.

The outputted size is not the size of each allocation, but the sum of
every allocation for a given stackframe.

R=erikchen@chromium.org

Bug: 753514
Change-Id: I1840f89d06a63e5f30af66da080ef7ea91d1715a
Reviewed-on: https://chromium-review.googlesource.com/664250Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501465}

chrome/profiling/json_exporter.cc

@@ -276,7 +276,8 @@ void WriteSizes(const UniqueAllocCount& alloc_counts, std::ostream& out) {
       out << ",\n";
     else
       first_time = false;
-    out << cur.first.size;
+    // Output the total size, which is size * count.
+    out << cur.first.size * cur.second;
   }
   out << "]";
 }

chrome/profiling/json_exporter_unittest.cc

@@ -375,7 +375,7 @@ TEST(ProfilingJsonExporterTest, Simple) {
   // Validate node allocated with |stack1|.
   EXPECT_EQ(2, counts->GetList()[node1].GetInt());
   EXPECT_EQ(0, types->GetList()[node1].GetInt());
-  EXPECT_EQ(20, sizes->GetList()[node1].GetInt());
+  EXPECT_EQ(40, sizes->GetList()[node1].GetInt());
   EXPECT_EQ(id1, backtraces->GetList()[node1].GetInt());
 
   // Validate node allocated with |stack2|.