Move constant definitions out embedder.h (#8498)

shell/platform/embedder/embedder.cc

@@ -39,6 +39,9 @@ extern const intptr_t kPlatformStrongDillSize;
 #include "flutter/shell/platform/embedder/embedder_thread_host.h"
 #include "flutter/shell/platform/embedder/platform_view_embedder.h"
 
+const int32_t kFlutterSemanticsNodeIdBatchEnd = -1;
+const int32_t kFlutterSemanticsCustomActionIdBatchEnd = -1;
+
 static FlutterEngineResult LogEmbedderError(FlutterEngineResult code,
                                             const char* name,
                                             const char* function,

shell/platform/embedder/embedder.h

@@ -343,7 +343,7 @@ typedef struct {
 
 // |FlutterSemanticsNode| ID used as a sentinel to signal the end of a batch of
 // semantics node updates.
-const int32_t kFlutterSemanticsNodeIdBatchEnd = -1;
+extern const int32_t kFlutterSemanticsNodeIdBatchEnd;
 
 // A node that represents some semantic data.
 //
@@ -414,7 +414,7 @@ typedef struct {
 
 // |FlutterSemanticsCustomAction| ID used as a sentinel to signal the end of a
 // batch of semantics custom action updates.
-const int32_t kFlutterSemanticsCustomActionIdBatchEnd = -1;
+extern const int32_t kFlutterSemanticsCustomActionIdBatchEnd;
 
 // A custom semantics action, or action override.
 //