DevTools: add network throttling presets to command menu

Screenshot: https://imgur.com/a/NN6xOYN

Bug: 784231
Change-Id: I799e76c74f6e08bd64b1213918c7ce30135c69fa
Reviewed-on: https://chromium-review.googlesource.com/1100314Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567752}

third_party/blink/renderer/devtools/front_end/mobile_throttling/ThrottlingManager.js

@@ -251,6 +251,14 @@ MobileThrottling.ThrottlingManager.ActionDelegate = class {
       SDK.multitargetNetworkManager.setNetworkConditions(SDK.NetworkManager.NoThrottlingConditions);
       return true;
     }
+    if (actionId === 'network-conditions.network-low-end-mobile') {
+      SDK.multitargetNetworkManager.setNetworkConditions(SDK.NetworkManager.Slow3GConditions);
+      return true;
+    }
+    if (actionId === 'network-conditions.network-mid-tier-mobile') {
+      SDK.multitargetNetworkManager.setNetworkConditions(SDK.NetworkManager.Fast3GConditions);
+      return true;
+    }
     if (actionId === 'network-conditions.network-offline') {
       SDK.multitargetNetworkManager.setNetworkConditions(SDK.NetworkManager.OfflineConditions);
       return true;

third_party/blink/renderer/devtools/front_end/mobile_throttling/module.json

@@ -12,7 +12,23 @@
             "category": "Network",
             "title": "Go offline",
             "className": "MobileThrottling.ThrottlingManager.ActionDelegate",
-            "tags": "device"
+            "tags": "device, throttling"
+        },
+        {
+            "type": "action",
+            "actionId": "network-conditions.network-low-end-mobile",
+            "category": "Network",
+            "title": "Enable slow 3G throttling",
+            "className": "MobileThrottling.ThrottlingManager.ActionDelegate",
+            "tags": "device, throttling"
+        },
+        {
+            "type": "action",
+            "actionId": "network-conditions.network-mid-tier-mobile",
+            "category": "Network",
+            "title": "Enable fast 3G throttling",
+            "className": "MobileThrottling.ThrottlingManager.ActionDelegate",
+            "tags": "device, throttling"
         },
         {
             "type": "action",
@@ -20,7 +36,7 @@
             "category": "Network",
             "title": "Go online",
             "className": "MobileThrottling.ThrottlingManager.ActionDelegate",
-            "tags": "device"
+            "tags": "device, throttling"
         },
         {
             "type": "view",