Diagnostics: Support reset on the fake provider

- Add reset method to fake provider
- Move method resolvers and observables to class methods

Tests are in a follow up CL

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: Ib36194af7511da82991a012325f6a12018d12239
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437027
Commit-Queue: Michael Checo <michaelcheco@google.com>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812121}

chromeos/components/diagnostics_ui/resources/fake_system_data_provider.js

@@ -19,16 +19,8 @@ export class FakeSystemDataProvider {
     /** @private {!FakeObservables} */
     this.observables_ = new FakeObservables();
 
-    // Setup method resolvers.
-    this.methods_.register('getSystemInfo');
-    this.methods_.register('getBatteryInfo');
-
-    // Setup observables.
-    this.observables_.register(
-        'BatteryChargeStatusObserver_onBatteryChargeStatusUpdated');
-    this.observables_.register('BatteryHealthObserver_onBatteryHealthUpdated');
-    this.observables_.register('CpuUsageObserver_onCpuUsageUpdated');
-    this.observables_.register('MemoryUsageObserver_onMemoryUsageUpdated');
+    this.registerMethods();
+    this.registerObservables();
   }
 
   /**
@@ -193,4 +185,36 @@ export class FakeSystemDataProvider {
   stopTriggerIntervals() {
     this.observables_.stopAllTriggerIntervals();
   }
+
+  /**
+   * Setup method resolvers.
+   */
+  registerMethods() {
+    this.methods_.register('getSystemInfo');
+    this.methods_.register('getBatteryInfo');
+  }
+
+  /**
+   * Setup observables.
+   */
+  registerObservables() {
+    this.observables_.register(
+    'BatteryChargeStatusObserver_onBatteryChargeStatusUpdated');
+    this.observables_.register('BatteryHealthObserver_onBatteryHealthUpdated');
+    this.observables_.register('CpuUsageObserver_onCpuUsageUpdated');
+    this.observables_.register('MemoryUsageObserver_onMemoryUsageUpdated');
+  }
+
+  /**
+   * Disables all observers and resets provider to its initial state.
+   */
+  reset() {
+    this.observables_.stopAllTriggerIntervals();
+
+    this.methods_ = new FakeMethodResolver();
+    this.observables_ = new FakeObservables();
+
+    this.registerMethods();
+    this.registerObservables();
+  }
 }