Add key() method to ToolchainContext.

Cleanup leading to toolchain transitions, #10523.

Closes #11337.

PiperOrigin-RevId: 311148682
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BUILD b/src/main/java/com/google/devtools/build/lib/analysis/BUILD
index e3e8b02..ad2a017 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BUILD
@@ -407,6 +407,7 @@
         "//src/main/java/com/google/devtools/build/lib/skyframe:configured_value_creation_exception",
         "//src/main/java/com/google/devtools/build/lib/skyframe:package_value",
         "//src/main/java/com/google/devtools/build/lib/skyframe:precomputed_value",
+        "//src/main/java/com/google/devtools/build/lib/skyframe:toolchain_context_key",
         "//src/main/java/com/google/devtools/build/lib/skyframe:toolchain_exception",
         "//src/main/java/com/google/devtools/build/lib/skyframe:transitive_target_key",
         "//src/main/java/com/google/devtools/build/lib/skyframe:transitive_target_value",
@@ -1018,6 +1019,7 @@
     deps = [
         "//src/main/java/com/google/devtools/build/lib/analysis/platform",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
+        "//src/main/java/com/google/devtools/build/lib/skyframe:toolchain_context_key",
         "//third_party:guava",
     ],
 )