Feature/bunny hop (#2647)

* `@0x/contracts-erc20-bridge-sampler`: Add TwoHopSampler + refactor

* `@0x/asset-swapper`: Refactor + add two-hop skeleton

* Round out two-hop support in asset-swapper

* Add BalancerSampler, use it for two-hop quotes

* Fix bugs discovered from simbot

* rebases are hard

* Add intermediate token to MultiHop source breakdown

* Fix market buy bugs

* Use hybrid on-chain/off-chain sampling for Balancer

* Another day, another rebase

* Update changelogs

* Address PR feedback, CI fixes

* Address more PR feedback

packages/asset-swapper/contracts/test/DummyLiquidityProvider.sol

@@ -0,0 +1,38 @@
+pragma solidity ^0.5.9;
+pragma experimental ABIEncoderV2;
+
+
+contract DummyLiquidityProvider
+{
+    /// @dev Quotes the amount of `makerToken` that would be obtained by
+    ///      selling `sellAmount` of `takerToken`.
+    /// @param sellAmount Amount of `takerToken` to sell.
+    /// @return makerTokenAmount Amount of `makerToken` that would be obtained.
+    function getSellQuote(
+        address, /* takerToken */
+        address, /* makerToken */
+        uint256 sellAmount
+    )
+        external
+        view
+        returns (uint256 makerTokenAmount)
+    {
+        makerTokenAmount = sellAmount - 1;
+    }
+
+    /// @dev Quotes the amount of `takerToken` that would need to be sold in
+    ///      order to obtain `buyAmount` of `makerToken`.
+    /// @param buyAmount Amount of `makerToken` to buy.
+    /// @return takerTokenAmount Amount of `takerToken` that would need to be sold.
+    function getBuyQuote(
+        address, /* takerToken */
+        address, /* makerToken */
+        uint256 buyAmount
+    )
+        external
+        view
+        returns (uint256 takerTokenAmount)
+    {
+        takerTokenAmount = buyAmount + 1;
+    }
+}

packages/asset-swapper/contracts/test/DummyLiquidityProviderRegistry.sol

@@ -0,0 +1,44 @@
+pragma solidity ^0.5.9;
+pragma experimental ABIEncoderV2;
+
+
+contract DummyLiquidityProviderRegistry
+{
+    address private constant NULL_ADDRESS = address(0x0);
+
+    mapping (address => mapping (address => address)) internal _gAddressBook;
+
+    /// @dev Sets address of pool for a market given market (xAsset, yAsset).
+    /// @param xToken First asset managed by pool.
+    /// @param yToken Second asset managed by pool.
+    /// @param poolAddress Address of pool.
+    function setLiquidityProviderForMarket(
+        address xToken,
+        address yToken,
+        address poolAddress
+    )
+        external
+    {
+        _gAddressBook[xToken][yToken] = poolAddress;
+        _gAddressBook[yToken][xToken] = poolAddress;
+    }
+
+    /// @dev Returns the address of pool for a market given market (xAsset, yAsset), or reverts if pool does not exist.
+    /// @param xToken First asset managed by pool.
+    /// @param yToken Second asset managed by pool.
+    /// @return Address of pool.
+    function getLiquidityProviderForMarket(
+        address xToken,
+        address yToken
+    )
+        external
+        view
+        returns (address poolAddress)
+    {
+        poolAddress = _gAddressBook[xToken][yToken];
+        require(
+            poolAddress != NULL_ADDRESS,
+            "Registry/MARKET_PAIR_NOT_SET"
+        );
+    }
+}

packages/asset-swapper/contracts/test/TestERC20BridgeSampler.sol

@@ -22,9 +22,9 @@ import "@0x/contracts-asset-proxy/contracts/src/interfaces/IUniswapExchangeFacto
 import "@0x/contracts-exchange/contracts/src/interfaces/IExchange.sol";
 import "@0x/contracts-exchange-libs/contracts/src/LibOrder.sol";
 import "../src/ERC20BridgeSampler.sol";
-import "../src/IEth2Dai.sol";
-import "../src/IKyberNetworkProxy.sol";
-import "../src/IUniswapV2Router01.sol";
+import "../src/interfaces/IEth2Dai.sol";
+import "../src/interfaces/IKyberNetworkProxy.sol";
+import "../src/interfaces/IUniswapV2Router01.sol";
 
 
 library LibDeterministicQuotes {