Add suffix to monolithic pipeline cache key

This is a workaround so that Chrome can identify the entry and handle it
specially, eg. record histograms about the size and not save it to the
memory cache.

Bug: 450577968, 508178495
Change-Id: I9e020f4046507f71b2474187a9d910c7150f49d7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/306055
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Kyle Charbonneau <kylechar@google.com>

src/dawn/native/vulkan/DeviceVk.cpp

diff --git a/src/dawn/native/vulkan/DeviceVk.cpp b/src/dawn/native/vulkan/DeviceVk.cpp
index 4dd4a96..5062c31 100644
--- a/src/dawn/native/vulkan/DeviceVk.cpp
+++ b/src/dawn/native/vulkan/DeviceVk.cpp
@@ -277,7 +277,11 @@
             // the serialized VkPipelineCache is no longer valid.
             auto& deviceProperties = GetDeviceInfo().properties;
             StreamIn(&cacheKey, deviceProperties.pipelineCacheUUID);
-
+            // A fixed string is added to the end of monolithic pipeline cache key in order to make
+            // it identifiable in the BlobCache storage implementation.
+            // TODO(crbug.com/508178495): Change the BlobCache API so that additional metadata about
+            // the cache entry can be included and remove this workaround.
+            StreamIn(&cacheKey, std::string_view("MonolithicVkPipelineCache"));
             mMonolithicPipelineCache = PipelineCache::CreateMonolithic(this, cacheKey);
         });