Report more detailed error information for the failures of mapAsync

This patch adds two new buffer map async status "destroyed before
callback" and "unmapped before callback" to replace the status "unknown"
so that the developers can get more details when meeting such errors in
the call of buffer mapAsync.

Note that this patch still preserves "unknown" as it is still being used
in Chromium.

BUG=dawn:533
TEST=dawn_unittests

Change-Id: I12deefb49311ea6adea72c24e4e40797dd7eb4a1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/28883
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

src/dawn_native/Buffer.cpp

diff --git a/src/dawn_native/Buffer.cpp b/src/dawn_native/Buffer.cpp
index 1a2fbc2..aa9af0a 100644
--- a/src/dawn_native/Buffer.cpp
+++ b/src/dawn_native/Buffer.cpp
@@ -138,7 +138,7 @@
     BufferBase::~BufferBase() {
         if (mState == BufferState::Mapped) {
             ASSERT(!IsError());
-            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown);
+            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
         }
     }
 
@@ -302,13 +302,13 @@
         ASSERT(!IsError());
 
         if (mState == BufferState::Mapped) {
-            Unmap();
+            UnmapInternal(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
         } else if (mState == BufferState::MappedAtCreation) {
             if (mStagingBuffer != nullptr) {
                 mStagingBuffer.reset();
             } else if (mSize != 0) {
                 ASSERT(IsCPUWritableAtCreation());
-                Unmap();
+                UnmapInternal(WGPUBufferMapAsyncStatus_DestroyedBeforeCallback);
             }
         }
 
@@ -330,6 +330,10 @@
     }
 
     void BufferBase::Unmap() {
+        UnmapInternal(WGPUBufferMapAsyncStatus_UnmappedBeforeCallback);
+    }
+
+    void BufferBase::UnmapInternal(WGPUBufferMapAsyncStatus callbackStatus) {
         if (IsError()) {
             // It is an error to call Unmap() on an ErrorBuffer, but we still need to reclaim the
             // fake mapped staging data.
@@ -346,7 +350,7 @@
             // completed before the Unmap.
             // Callbacks are not fired if there is no callback registered, so this is correct for
             // mappedAtCreation = true.
-            CallMapCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown);
+            CallMapCallback(mMapSerial, callbackStatus);
             UnmapImpl();
 
             mMapCallback = nullptr;