Add hex-prefix to gas estimate result

ui/app/components/send_/send.utils.js

@@ -201,12 +201,12 @@ async function estimateGas ({ selectedAddress, selectedToken, blockGasLimit, to,
           err.message.includes('gas required exceeds allowance or always failing transaction')
         )
         if (simulationFailed) {
-          return resolve(paramsForGasEstimate.gas)
+          return resolve(ethUtil.addHexPrefix(paramsForGasEstimate.gas))
         } else {
           return reject(err)
         }
       }
-      return resolve(estimatedGas.toString(16))
+      return resolve(ethUtil.addHexPrefix(estimatedGas.toString(16)))
     })
   })
 }

ui/app/components/send_/tests/send-utils.test.js

@@ -285,7 +285,7 @@ describe('send utils', () => {
         baseMockParams.estimateGasMethod.getCall(0).args[0],
         Object.assign({ gasPrice: undefined, value: undefined }, baseExpectedCall)
       )
-      assert.equal(result, 'mockToString:16')
+      assert.equal(result, '0xmockToString:16')
     })
 
     it('should call ethQuery.estimateGas with a value of 0x0 and the expected data and to if passed a selectedToken', async () => {
@@ -300,7 +300,7 @@ describe('send utils', () => {
           to: 'mockAddress',
         })
       )
-      assert.equal(result, 'mockToString:16')
+      assert.equal(result, '0xmockToString:16')
     })
 
     it(`should return ${SIMPLE_GAS_COST} if ethQuery.getCode does not return '0x'`, async () => {