Capture/Replay: Ignore delete of non-genned buffers

Instead of asserting that the app is calling glDeleteBuffers
on buffers we've seen created, ignore buffer names that we
haven't seen. This is allowed by the spec:

  Buffer objects are deleted by calling
    void DeleteBuffers(sizei n, const uint *buffers);
  Unused names in buffers are silently ignored, as is the value zero.

Test: SAKURA School Simulator MEC
Bug: b/188488065
Bug: angleproject:5987
Change-Id: Id4704e544f644dbe3edf6efdf70b5c3ef9ccaba7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2902442
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Cody Northrop <cnorthrop@google.com>

src/libANGLE/capture/FrameCapture.cpp

@@ -4939,13 +4939,16 @@ void ResourceTracker::setDeletedBuffer(gl::BufferID id)
         return;
     }
 
-    // Ensure this buffer was in our starting set
-    // It's possible this could fire if the app deletes buffers that were never generated
-    ASSERT(mStartingBuffers.empty() || (mStartingBuffers.find(id) != mStartingBuffers.end()));
+    if (mStartingBuffers.find(id) != mStartingBuffers.end())
+    {
+        // The app is deleting a buffer we started with, we need to regen on loop
+        mBuffersToRegen.insert(id);
+        mBuffersToRestore.insert(id);
+    }
 
-    // In this case, the app is deleting a buffer we started with, we need to regen on loop
-    mBuffersToRegen.insert(id);
-    mBuffersToRestore.insert(id);
+    // If none of the above is true, the app is deleting a buffer that was never genned.
+    // This is allowed by the spec for DeleteBuffers:
+    //    Unused names in buffers are silently ignored, as is the value zero.
 }
 
 void ResourceTracker::setDeletedFenceSync(GLsync sync)