vulkan: Allow drivers to add private gralloc usage flags

Change-Id: Iea33990b3a85a761e27d54bb323d866267c88901
(cherry picked from commit c040fbedde52d632a7ceeef3a9266d35b22ce53f)
diff --git a/vulkan/nulldrv/null_driver.h b/vulkan/nulldrv/null_driver.h
index 28f294d..6cf0afd 100644
--- a/vulkan/nulldrv/null_driver.h
+++ b/vulkan/nulldrv/null_driver.h
@@ -172,6 +172,7 @@
 void CmdEndRenderPass(VkCmdBuffer cmdBuffer);
 void CmdExecuteCommands(VkCmdBuffer cmdBuffer, uint32_t cmdBuffersCount, const VkCmdBuffer* pCmdBuffers);
 
+VkResult GetSwapchainGrallocUsageANDROID(VkDevice device, VkFormat format, VkImageUsageFlags imageUsage, int* grallocUsage);
 VkResult ImportNativeFenceANDROID(VkDevice device, VkSemaphore semaphore, int nativeFenceFd);
 VkResult QueueSignalNativeFenceANDROID(VkQueue queue, int* pNativeFenceFd);
 // clang-format on