cc: Prevent integer overflow with software TextureMailbox.

cc/resources/texture_mailbox.h

Index: cc/resources/texture_mailbox.h
diff --git a/cc/resources/texture_mailbox.h b/cc/resources/texture_mailbox.h
index e29004268f4b875eeecfbfee18ad28b336570a27..2bc1fd604e798cfb1be4d5f8af8d4bf7d66509d6 100644
--- a/cc/resources/texture_mailbox.h
+++ b/cc/resources/texture_mailbox.h
@@ -9,6 +9,7 @@
 
 #include "base/callback.h"
 #include "base/memory/shared_memory.h"
+#include "base/numerics/safe_math.h"
 #include "cc/base/cc_export.h"
 #include "gpu/command_buffer/common/mailbox_holder.h"
 #include "ui/gfx/size.h"
@@ -45,7 +46,9 @@ class CC_EXPORT TextureMailbox {
 
   base::SharedMemory* shared_memory() const { return shared_memory_; }
   gfx::Size shared_memory_size() const { return shared_memory_size_; }
-  size_t shared_memory_size_in_bytes() const;
+
+  size_t SharedMemorySizeInBytes() const;
+  base::CheckedNumeric<size_t> CheckedSharedMemorySizeInBytes() const;
 
  private:
   gpu::MailboxHolder mailbox_holder_;