Add a CpuWritesGpuReadsCached finch flag

In this CL, we want to relax the requirement for CACHED memory as part
of a finch experiment. On Mali GPU, we have roughly 3 types:

    a) HOST | COHERENT| DEVICE (coherent is not cached)
    b) HOST | CACHED | DEVICE  (cached is non-coherent)
    c) DEVICE

By relaxing the CACHED condition, the driver is free to give
us (a) or (b) based on what it thinks is more performant.
This is roughtly equivalent to
https://skia-review.googlesource.com/c/skia/+/312056

Change-Id: Ib8a76b1870b6284ba1cb83128f5349e96f56fc9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2376447Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Jonathan Backer <backer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801624}

gpu/vulkan/init/gr_vk_memory_allocator_impl.cc

@@ -6,6 +6,7 @@
 
 #include <vk_mem_alloc.h>
 
+#include "base/feature_list.h"
 #include "base/trace_event/trace_event.h"
 #include "gpu/vulkan/vma_wrapper.h"
 #include "gpu/vulkan/vulkan_device_queue.h"
@@ -14,6 +15,9 @@ namespace gpu {
 
 namespace {
 
+const base::Feature kCpuWritesGpuReadsCached{"CpuWritesGpuReadsCached",
+                                             base::FEATURE_ENABLED_BY_DEFAULT};
+
 class GrVkMemoryAllocatorImpl : public GrVkMemoryAllocator {
  public:
   explicit GrVkMemoryAllocatorImpl(VmaAllocator allocator)
@@ -82,9 +86,10 @@ class GrVkMemoryAllocatorImpl : public GrVkMemoryAllocator {
         info.preferredFlags = VK_MEMORY_PROPERTY_HOST_CACHED_BIT;
         break;
       case BufferUsage::kCpuWritesGpuReads:
-        // First attempt to try memory is also cached
-        info.requiredFlags = VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
-                             VK_MEMORY_PROPERTY_HOST_CACHED_BIT;
+        info.requiredFlags = VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT;
+        if (base::FeatureList::IsEnabled(kCpuWritesGpuReadsCached))
+          info.requiredFlags |= VK_MEMORY_PROPERTY_HOST_CACHED_BIT;
+
         info.preferredFlags = VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT;
         break;
       case BufferUsage::kGpuWritesCpuReads:
@@ -217,4 +222,4 @@ sk_sp<GrVkMemoryAllocator> CreateGrVkMemoryAllocator(
   return sk_make_sp<GrVkMemoryAllocatorImpl>(device_queue->vma_allocator());
 }
 
-}  // namespace gpu
+}  // namespace gpu
\ No newline at end of file