Promisify gas estimation (#8387)

The `estimateGasMethod` function passed to `estimateGas` is now an
async function. It is now invoked using `async/await` rather than a
Promise constructor.

This was done as part of a broader effort to use Promises rather than
callbacks when interacting with the background.

ui/app/pages/send/send.utils.js

@@ -256,24 +256,22 @@ async function estimateGas ({
   }))
 
   // run tx
-  return new Promise((resolve, reject) => {
-    return estimateGasMethod(paramsForGasEstimate, (err, estimatedGas) => {
-      if (err) {
-        const simulationFailed = (
-          err.message.includes('Transaction execution error.') ||
-          err.message.includes('gas required exceeds allowance or always failing transaction')
-        )
-        if (simulationFailed) {
-          const estimateWithBuffer = addGasBuffer(paramsForGasEstimate.gas, blockGasLimit, 1.5)
-          return resolve(ethUtil.addHexPrefix(estimateWithBuffer))
-        } else {
-          return reject(err)
-        }
-      }
-      const estimateWithBuffer = addGasBuffer(estimatedGas.toString(16), blockGasLimit, 1.5)
-      return resolve(ethUtil.addHexPrefix(estimateWithBuffer))
-    })
-  })
+  try {
+    const estimatedGas = await estimateGasMethod(paramsForGasEstimate)
+    const estimateWithBuffer = addGasBuffer(estimatedGas.toString(16), blockGasLimit, 1.5)
+    return ethUtil.addHexPrefix(estimateWithBuffer)
+  } catch (error) {
+    const simulationFailed = (
+      error.message.includes('Transaction execution error.') ||
+      error.message.includes('gas required exceeds allowance or always failing transaction')
+    )
+    if (simulationFailed) {
+      const estimateWithBuffer = addGasBuffer(paramsForGasEstimate.gas, blockGasLimit, 1.5)
+      return ethUtil.addHexPrefix(estimateWithBuffer)
+    } else {
+      throw error
+    }
+  }
 }
 
 function addGasBuffer (initialGasLimitHex, blockGasLimitHex, bufferMultiplier = 1.5) {

ui/app/pages/send/tests/send-utils.test.js

@@ -301,12 +301,11 @@ describe('send utils', function () {
       selectedAddress: 'mockAddress',
       to: '0xisContract',
       estimateGasMethod: sinon.stub().callsFake(
-        ({ to }, cb) => {
-          const err = typeof to === 'string' && to.match(/willFailBecauseOf:/)
-            ? new Error(to.match(/:(.+)$/)[1])
-            : null
-          const result = { toString: (n) => `0xabc${n}` }
-          return cb(err, result)
+        ({ to }) => {
+          if (typeof to === 'string' && to.match(/willFailBecauseOf:/)) {
+            throw new Error(to.match(/:(.+)$/)[1])
+          }
+          return { toString: (n) => `0xabc${n}` }
         }
       ),
     }

ui/app/store/actions.js

@@ -653,7 +653,7 @@ export function updateGasData ({
   return (dispatch) => {
     dispatch(gasLoadingStarted())
     return estimateGas({
-      estimateGasMethod: background.estimateGas,
+      estimateGasMethod: promisifiedBackground.estimateGas,
       blockGasLimit,
       selectedAddress,
       selectedToken,