Add comments for struct members that were changed from size_t to uin32_t or uint64_t for IPC safety.

content/common/gpu/gpu_memory_uma_stats.h

Index: content/common/gpu/gpu_memory_uma_stats.h
diff --git a/content/common/gpu/gpu_memory_uma_stats.h b/content/common/gpu/gpu_memory_uma_stats.h
index 16c8813544a99769924ffbaa398dda9f0179debc..779b57166df588d35950b7e38b77473a70c1dbe4 100644
--- a/content/common/gpu/gpu_memory_uma_stats.h
+++ b/content/common/gpu/gpu_memory_uma_stats.h
@@ -11,6 +11,8 @@ namespace content {
 
 // Memory usage statistics send periodically to the browser process to report
 // in UMA histograms if the GPU process crashes.
+// Note: we use uint64_t instead of size_t for byte count because this struct
+// is sent over IPC which could span 32 & 64 bit processes.
 struct GPUMemoryUmaStats {
   GPUMemoryUmaStats()
       : bytes_allocated_current(0),
@@ -19,10 +21,10 @@ struct GPUMemoryUmaStats {
   }
 
   // The number of bytes currently allocated.
-  uint32_t bytes_allocated_current;
+  uint64_t bytes_allocated_current;
 
   // The maximum number of bytes ever allocated at once.
-  uint32_t bytes_allocated_max;
+  uint64_t bytes_allocated_max;
 
   // The number of context groups.
   uint32_t context_group_count;