Log chromium event for automatic dynamic reasons (pytorch#137491)

Log a chromium event so that we can see the reasons for invoking automatic dynamic shapes in aggregate internally.

Run following code:
```
import torch
@torch.compile(backend="eager")
def foo(t, x):
    return t.sin() + x

torch._dynamo.config.automatic_dynamic_shapes = True
torch._dynamo.config.assume_static_by_default = True
# Change size
x = torch.randn([1,2])
foo(x, 2)
x = torch.randn([2,2])
foo(x, 2)
torch._dynamo.reset()
# Change dimensionality
x = torch.randn([1,2])
foo(x, 2)
x = torch.randn([1,2,3])
foo(x, 2)
torch._dynamo.reset()
# Change stride
x = torch.randn([3,3])
foo(x, 2)
x = torch.as_strided(x, [3,3], [2,2])
foo(x, 2)
torch._dynamo.reset()
# Change scalar
x = torch.randn([1,2])
foo(x, 2)
foo(x, 3)
```

Internal link to perfetto:
https://interncache-all.fbcdn.net/manifold/perfetto-artifacts/tree/ui/index.html?url=https%3A%2F%2Finterncache-all.fbcdn.net%2Fmanifold%2Ftlparse_reports%2Ftree%2Flogs%2Fjjwu%2Fcustom%2Fchromium_events.json#!/viewer?url=https%3A%2F%2Finterncache-all.fbcdn.net%2Fmanifold%2Ftlparse_reports%2Ftree%2Flogs%2Fjjwu%2Fcustom%2Fchromium_events.json&local_cache_key

The events look like this:
<img width="639" alt="image" src="https://github.com/user-attachments/assets/23916333-7f24-47c7-934b-201f33aebeab">
<img width="638" alt="image" src="https://github.com/user-attachments/assets/9f927c8d-04bb-4431-8802-685b032df656">
<img width="640" alt="image" src="https://github.com/user-attachments/assets/342e9e11-0dfc-422d-bd0b-01a8574d38ba">
<img width="635" alt="image" src="https://github.com/user-attachments/assets/dc2c97cd-7180-4069-b019-d6e63ee490bc">

Differential Revision: [D64184625](https://our.internmc.facebook.com/intern/diff/D64184625)
Pull Request resolved: pytorch#137491
Approved by: https://github.com/Skylion007, https://github.com/oulgen

Author: jamesjwu

torch/_dynamo/variables/builder.py

@@ -14,6 +14,7 @@
 import random
 import re
 import sys
+import time
 import types
 import warnings
 import weakref
@@ -33,6 +34,7 @@
 
 import torch
 from torch import SymInt
+from torch._dynamo.utils import get_chromium_event_logger
 from torch._guards import GuardSource, TracingContext
 from torch._higher_order_ops.torchbind import call_torchbind
 from torch._ops import HigherOrderOperator
@@ -1760,6 +1762,17 @@ def update_frame_state(value):
                             value,
                             frame_state_entry.scalar,
                         )
+                        get_chromium_event_logger().log_instant_event(
+                            "automatic_dynamic",
+                            time.time_ns(),
+                            {
+                                "name": name,
+                                "dim_changed": "scalar",
+                                "reason": "scalar change",
+                                "cached": str(frame_state_entry.scalar),
+                                "new": str(value),
+                            },
+                        )
                         if self.source.guard_source().is_unspecialized_nn_module():
                             log.info(
                                 "%s",
@@ -2466,6 +2479,17 @@ def update_frame_state(size, stride):
                         len(size),
                         frame_state_entry.size,
                     )
+                    get_chromium_event_logger().log_instant_event(
+                        "automatic_dynamic",
+                        time.time_ns(),
+                        {
+                            "name": name,
+                            "dim_changed": "all",
+                            "reason": "dimensionality change",
+                            "cached": str(frame_state_entry.size),
+                            "new": str(size),
+                        },
+                    )
                     frame_state_entry.size = None
                     frame_state_entry.stride = None
                 else:
@@ -2483,6 +2507,17 @@ def update_frame_state(size, stride):
                                 size[i],
                                 dim,
                             )
+                            get_chromium_event_logger().log_instant_event(
+                                "automatic_dynamic",
+                                time.time_ns(),
+                                {
+                                    "name": name,
+                                    "dim_changed": i,
+                                    "reason": "size change",
+                                    "cached": str(dim),
+                                    "new": str(size[i]),
+                                },
+                            )
                             frame_state_entry.size[i] = None
                         has_size_changed = (
                             has_size_changed or frame_state_entry.size[i] is None
@@ -2513,6 +2548,17 @@ def update_frame_state(size, stride):
                                     stride[i],
                                     dim,
                                 )
+                                get_chromium_event_logger().log_instant_event(
+                                    "automatic_dynamic",
+                                    time.time_ns(),
+                                    {
+                                        "name": name,
+                                        "dim_changed": i,
+                                        "reason": "stride change",
+                                        "cached": str(dim),
+                                        "new": str(stride[i]),
+                                    },
+                                )
                                 frame_state_entry.stride[i] = None
         tx.output.frame_state[name] = frame_state_entry