Remove Transferable type as a global and put it in the types folder.

src/data/bucket.js

@@ -6,6 +6,7 @@ import type CollisionBoxArray from '../symbol/collision_box';
 import type Style from '../style/style';
 import type StyleLayer from '../style/style_layer';
 import type FeatureIndex from './feature_index';
+import type {Transferable} from '../types/transferable';
 
 export type BucketParameters = {
     index: number,

src/data/bucket/circle_bucket.js

@@ -14,6 +14,7 @@ import type {ProgramInterface} from '../program_configuration';
 import type StyleLayer from '../../style/style_layer';
 import type {StructArray} from '../../util/struct_array';
 import type Point from '@mapbox/point-geometry';
+import type {Transferable} from '../../types/transferable';
 
 const circleInterface = {
     layoutAttributes: [

src/data/bucket/fill_bucket.js

@@ -17,6 +17,7 @@ import type {ProgramInterface} from '../program_configuration';
 import type StyleLayer from '../../style/style_layer';
 import type {StructArray} from '../../util/struct_array';
 import type Point from '@mapbox/point-geometry';
+import type {Transferable} from '../../types/transferable';
 
 const fillInterface = {
     layoutAttributes: [

src/data/bucket/fill_extrusion_bucket.js

@@ -18,6 +18,7 @@ import type {ProgramInterface} from '../program_configuration';
 import type StyleLayer from '../../style/style_layer';
 import type {StructArray} from '../../util/struct_array';
 import type Point from '@mapbox/point-geometry';
+import type {Transferable} from '../../types/transferable';
 
 const fillExtrusionInterface = {
     layoutAttributes: [

src/data/bucket/line_bucket.js

@@ -16,6 +16,7 @@ import type LineStyleLayer from '../../style/style_layer/line_style_layer';
 import type Point from '@mapbox/point-geometry';
 import type {Segment} from '../segment';
 import type {StructArray} from '../../util/struct_array';
+import type {Transferable} from '../../types/transferable';
 
 // NOTE ON EXTRUDE SCALE:
 // scale the extrusion vector so that the normal length is this value.

src/data/bucket/symbol_bucket.js

@@ -30,6 +30,7 @@ import type SymbolStyleLayer from '../../style/style_layer/symbol_style_layer';
 import type {SymbolQuad} from '../../symbol/quads';
 import type {SizeData} from '../../symbol/symbol_size';
 import type {PossiblyEvaluatedPropertyValue} from '../../style/properties';
+import type {Transferable} from '../../types/transferable';
 
 export type SingleCollisionBox = {
     x1: number;

src/data/feature_index.js

@@ -17,6 +17,7 @@ import type CollisionIndex from '../symbol/collision_index';
 import type StyleLayer from '../style/style_layer';
 import type {SerializedStructArray} from '../util/struct_array';
 import type {FeatureFilter} from '../style-spec/feature_filter';
+import type {Transferable} from '../types/transferable';
 
 const FeatureIndexArray = createStructArrayType({
     members: [

src/data/program_configuration.js

@@ -12,6 +12,7 @@ import type {ViewType, StructArray, SerializedStructArray, StructArrayTypeParame
 import type Program from '../render/program';
 import type {Feature, SourceExpression, CompositeExpression} from '../style-spec/expression';
 import type {PossiblyEvaluated, PossiblyEvaluatedPropertyValue} from '../style/properties';
+import type {Transferable} from '../types/transferable';
 
 type LayoutAttribute = {
     name: string,

src/source/worker_source.js

@@ -6,6 +6,7 @@ import type {SerializedFeatureIndex} from '../data/feature_index';
 import type {SerializedStructArray} from '../util/struct_array';
 import type {RequestParameters} from '../util/ajax';
 import type {RGBAImage, AlphaImage} from '../util/image';
+import type {Transferable} from '../types/transferable';
 
 export type TileParameters = {
     source: string,

src/source/worker_tile.js

@@ -21,6 +21,7 @@ import type {
     WorkerTileParameters,
     WorkerTileCallback,
 } from '../source/worker_source';
+import type {Transferable} from '../types/transferable';
 
 class WorkerTile {
     coord: TileCoord;

src/types/transferable.js

@@ -0,0 +1,3 @@
+// @flow
+
+export type Transferable = ArrayBuffer | MessagePort | ImageBitmap;

src/util/actor.js

@@ -2,6 +2,8 @@
 
 const util = require('./util');
 
+import type {Transferable} from '../types/transferable';
+
 /**
  * An implementation of the [Actor design pattern](http://en.wikipedia.org/wiki/Actor_model)
  * that maintains the relationship between asynchronous tasks and the objects

src/util/dispatcher.js

@@ -4,6 +4,7 @@ const util = require('./util');
 const Actor = require('./actor');
 
 import type WorkerPool from './worker_pool';
+import type {Transferable} from '../types/transferable';
 
 /**
  * Responsible for sending messages from a {@link Source} to an associated

src/util/struct_array.js

@@ -4,6 +4,8 @@
 
 const assert = require('assert');
 
+import type {Transferable} from '../types/transferable';
+
 module.exports = createStructArrayType;
 
 const viewTypes = {