Adds toggle to disable blob cache.

- The disable toggle will supercede the enable one once Chromium side
  deprecates usage of the enable one.

Bug: dawn:549
Change-Id: I5c5bd60161917fe2654cfce55a6f29e8a7e79962
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/110728
Commit-Queue: Loko Kung <lokokung@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/dawn/native/Device.cpp

@@ -618,7 +618,7 @@ BlobCache* DeviceBase::GetBlobCache() {
     // TODO(crbug.com/dawn/1481): Shader caching currently has a dependency on the WGSL writer to
     // generate cache keys. We can lift the dependency once we also cache frontend parsing,
     // transformations, and reflection.
-    if (IsToggleEnabled(Toggle::EnableBlobCache)) {
+    if (IsToggleEnabled(Toggle::EnableBlobCache) && !IsToggleEnabled(Toggle::DisableBlobCache)) {
         return mAdapter->GetInstance()->GetBlobCache();
     }
 #endif

src/dawn/native/Toggles.cpp

@@ -261,6 +261,12 @@ static constexpr ToggleEnumAndInfoList kToggleNameAndInfoList = {{
       "mips (level >= 2) doesn't work correctly. Workaround this issue by detecting this case and "
       "rendering to a temporary texture instead (with copies before and after if needed).",
       "https://crbug.com/dawn/1071"}},
+    {Toggle::DisableBlobCache,
+     {"disable_blob_cache",
+      "Disables usage of the blob cache (backed by the platform cache if set/passed). Prevents any "
+      "persistent caching capabilities, i.e. pipeline caching.",
+      "https://crbug.com/dawn/549"}},
+    // TODO(dawn:549) Remove after deprecating usage on the Chromium side.
     {Toggle::EnableBlobCache,
      {"enable_blob_cache",
       "Enables usage of the blob cache (backed by the platform cache if set/passed). Necessary for "

src/dawn/native/Toggles.h

@@ -72,6 +72,7 @@ enum class Toggle {
     VulkanUseZeroInitializeWorkgroupMemoryExtension,
     D3D12SplitBufferTextureCopyForRowsPerImagePaddings,
     MetalRenderR8RG8UnormSmallMipToTempTexture,
+    DisableBlobCache,
     EnableBlobCache,
     D3D12ForceClearCopyableDepthStencilTextureOnCreation,
     D3D12DontSetClearValueOnDepthTextureCreation,