[Cellular] Remove automatic cellular network scans.

Scans for cellular networks are disruptive and should be initiated
only by explicit user action. This CL does the following:
* Document that cellular scans should be explicit.
* Remove the periodic scan for all network types in network-select.
* Make sure that cellular scans are initiated only when
  cellular type is explicitly requested.
* Prevent network subpage from triggering cellular scans.

BUG=b/157403230

Change-Id: I3d70ede85b155346fe294bbfc0a0337c1e8c7408
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2217708Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Azeem Arshad <azeemarshad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772764}

chrome/browser/resources/settings/chromeos/internet_page/internet_subpage.js

@@ -261,7 +261,9 @@ Polymer({
     const INTERVAL_MS = 10 * 1000;
     let type = this.deviceState.type;
     if (type == mojom.NetworkType.kCellular && this.tetherDeviceState) {
-      type = mojom.NetworkType.kMobile;
+      // Only request tether scan. Cellular scan is disruptive and should
+      // only be triggered by explicit user action.
+      type = mojom.NetworkType.kTether;
     }
     this.networkConfig_.requestNetworkScan(type);
     this.scanIntervalId_ = window.setInterval(() => {

chromeos/network/network_state_handler.cc

@@ -1060,13 +1060,12 @@ void NetworkStateHandler::RequestScan(const NetworkTypePattern& type) {
     else if (type.Equals(NetworkTypePattern::WiFi()))
       return;  // Skip notify if disabled and wifi only requested.
   }
-  if (type.Equals(NetworkTypePattern::Cellular()) ||
-      type.Equals(NetworkTypePattern::Mobile())) {
-    // Only request a Cellular scan if Cellular or Mobile is requested
-    // explicitly.
+
+  if (type.Equals(NetworkTypePattern::Cellular())) {
+    // Only request a Cellular scan if Cellular is requested explicitly.
     if (IsTechnologyEnabled(NetworkTypePattern::Cellular()))
       shill_property_handler_->RequestScanByType(shill::kTypeCellular);
-    else if (type.Equals(NetworkTypePattern::Cellular()))
+    else
       return;  // Skip notify if disabled and cellular only requested.
   }
 

chromeos/network/network_state_handler.h

@@ -316,8 +316,10 @@ class COMPONENT_EXPORT(CHROMEOS_NETWORK) NetworkStateHandler
                            DeviceStateList* list) const;
 
   // Requests a network scan. This may trigger updates to the network
-  // list, which will trigger the appropriate observer calls. If |type| is
-  // Cellular, a mobile network scan will be requested if supported.
+  // list, which will trigger the appropriate observer calls.
+  // Note: If |type| is Cellular, a mobile network scan will be requested
+  // if supported. This is disruptive and should only be triggered by an
+  // explicit user action.
   void RequestScan(const NetworkTypePattern& type);
 
   // Requests an update for an existing NetworkState, e.g. after configuring

chromeos/services/network_config/public/mojom/cros_network_config.mojom

@@ -893,6 +893,9 @@ interface CrosNetworkConfig {
 
   // Requests a scan for new networks. If the list updates,
   // CrosNetworkConfigObserver::OnNetworkStateListChanged() will be signaled.
+  // Note: If |type| is Cellular, a mobile network scan will be requested
+  // if supported. This is disruptive and should only be triggered by an
+  // explicit user action.
   RequestNetworkScan(NetworkType type);
 
   // Returns the global policy properties. These properties are not expected to

ui/webui/resources/cr_components/chromeos/network/network_select.js

@@ -95,10 +95,13 @@ Polymer({
     this.refreshNetworks();
 
     const INTERVAL_MS = 10 * 1000;
-    const kAll = chromeos.networkConfig.mojom.NetworkType.kAll;
-    this.networkConfig_.requestNetworkScan(kAll);
+    // Request only WiFi network scans. Tether and Cellular scans are not useful
+    // here. Cellular scans are disruptive and should only be triggered by
+    // explicit user action.
+    const kWiFi = chromeos.networkConfig.mojom.NetworkType.kWiFi;
+    this.networkConfig_.requestNetworkScan(kWiFi);
     this.scanIntervalId_ = window.setInterval(function() {
-      this.networkConfig_.requestNetworkScan(kAll);
+      this.networkConfig_.requestNetworkScan(kWiFi);
     }.bind(this), INTERVAL_MS);
   },