D3D12: Support caching DX shaders.

This change is a prerequisite to D3D pipeline caching.

This change introduces:
- Caching interface which enables the cache.
- Helper for backends to load/store blobs to be cached.
- Ability to cache HLSL shaders.

Bug:dawn:549
Change-Id: I2af759882d18b3f45dc63e49dcb6a3caa1be3485
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/32305
Commit-Queue: Bryan Bernhart <bryan.bernhart@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn_platform/BUILD.gn

@@ -31,4 +31,9 @@ dawn_component("dawn_platform") {
   ]
 
   deps = [ "${dawn_root}/src/common" ]
+
+  public_deps = [
+    # DawnPlatform.h has #include <dawn/webgpu.h>
+    "${dawn_root}/src/dawn:dawn_headers",
+  ]
 }

src/dawn_platform/CMakeLists.txt

@@ -27,4 +27,4 @@ target_sources(dawn_platform PRIVATE
     "tracing/EventTracer.h"
     "tracing/TraceEvent.h"
 )
-target_link_libraries(dawn_platform PRIVATE dawn_internal_config dawn_common)
+target_link_libraries(dawn_platform PUBLIC dawn_headers PRIVATE dawn_internal_config dawn_common)

src/dawn_platform/DawnPlatform.cpp

@@ -14,10 +14,45 @@
 
 #include "dawn_platform/DawnPlatform.h"
 
+#include "common/Assert.h"
+
 namespace dawn_platform {
 
+    CachingInterface::CachingInterface() = default;
+
+    CachingInterface::~CachingInterface() = default;
+
     Platform::Platform() = default;
 
     Platform::~Platform() = default;
 
+    const unsigned char* Platform::GetTraceCategoryEnabledFlag(TraceCategory category) {
+        static unsigned char disabled = 0;
+        return &disabled;
+    }
+
+    double Platform::MonotonicallyIncreasingTime() {
+        return 0;
+    }
+
+    uint64_t Platform::AddTraceEvent(char phase,
+                                     const unsigned char* categoryGroupEnabled,
+                                     const char* name,
+                                     uint64_t id,
+                                     double timestamp,
+                                     int numArgs,
+                                     const char** argNames,
+                                     const unsigned char* argTypes,
+                                     const uint64_t* argValues,
+                                     unsigned char flags) {
+        // AddTraceEvent cannot be called if events are disabled.
+        ASSERT(false);
+        return 0;
+    }
+
+    dawn_platform::CachingInterface* Platform::GetCachingInterface(const void* fingerprint,
+                                                                   size_t fingerprintSize) {
+        return nullptr;
+    }
+
 }  // namespace dawn_platform