Modify gas price statistics (#2947)

* gas price distribution + median + tests

* put histogram in util

* use the util histogram

* remove the default gas price implementation

* histogram rpc

* fix empty corpus

* Add JS ethcore_gasPriceHistogram

* Fix typo (s/types/type/) & subsequent failing test

* Fix return type & formatting

* bucketBounds

* Add jsapi e2e test verification

js/src/api/rpc/ethcore/ethcore.e2e.js

@@ -27,6 +27,16 @@ describe('ethapi.ethcore', () => {
     });
   });
 
+  describe('gasPriceHistogram', () => {
+    it('returns and translates the target', () => {
+      return ethapi.ethcore.gasPriceHistogram().then((result) => {
+        expect(Object.keys(result)).to.deep.equal(['bucketBounds', 'counts']);
+        expect(result.bucketBounds.length > 0).to.be.true;
+        expect(result.counts.length > 0).to.be.true;
+      });
+    });
+  });
+
   describe('netChain', () => {
     it('returns and the chain', () => {
       return ethapi.ethcore.netChain().then((value) => {

js/src/api/rpc/ethcore/ethcore.js

@@ -15,7 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 import { inAddress, inData, inNumber16 } from '../../format/input';
-import { outAddress, outNumber, outPeers } from '../../format/output';
+import { outAddress, outHistogram, outNumber, outPeers } from '../../format/output';
 
 export default class Ethcore {
   constructor (transport) {
@@ -69,6 +69,12 @@ export default class Ethcore {
       .then(outNumber);
   }
 
+  gasPriceHistogram () {
+    return this._transport
+      .execute('ethcore_gasPriceHistogram')
+      .then(outHistogram);
+  }
+
   generateSecretPhrase () {
     return this._transport
       .execute('ethcore_generateSecretPhrase');