Introduce DeviceInfo as a new native module

Summary:
The `UIManager` already has a lot of responsibilities and is deeply
tied with React Native's view architecture. This diff separates out a
`DeviceInfo` native module to provide information about screen dimensions and
font scale, etc.

Reviewed By: fkgozali

Differential Revision: D4713834

fbshipit-source-id: f2ee93acf876a4221c29a8c731f5abeffbb97974

ReactAndroid/src/main/java/com/facebook/react/modules/deviceinfo/BUCK

@@ -0,0 +1,17 @@
+include_defs("//ReactAndroid/DEFS")
+
+android_library(
+    name = "deviceinfo",
+    srcs = glob(["**/*.java"]),
+    visibility = [
+        "PUBLIC",
+    ],
+    deps = [
+        react_native_dep("third-party/java/jsr-305:jsr-305"),
+        react_native_target("java/com/facebook/react/bridge:bridge"),
+        react_native_target("java/com/facebook/react/common:common"),
+        react_native_target("java/com/facebook/react/module/annotations:annotations"),
+        react_native_target("java/com/facebook/react/modules/core:core"),
+        react_native_target("java/com/facebook/react/uimanager:uimanager"),
+    ],
+)

ReactAndroid/src/main/java/com/facebook/react/modules/deviceinfo/DeviceInfoModule.java

@@ -0,0 +1,105 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.modules.deviceinfo;
+
+import javax.annotation.Nullable;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import android.util.DisplayMetrics;
+
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.LifecycleEventListener;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.module.annotations.ReactModule;
+import com.facebook.react.modules.core.DeviceEventManagerModule;
+import com.facebook.react.uimanager.DisplayMetricsHolder;
+
+/**
+ * Module that exposes Android Constants to JS.
+ */
+@ReactModule(name = "DeviceInfo")
+public class DeviceInfoModule extends ReactContextBaseJavaModule implements
+    LifecycleEventListener {
+
+  private float mFontScale;
+
+  public DeviceInfoModule(
+      ReactApplicationContext reactContext) {
+    super(reactContext);
+
+    mFontScale = getReactApplicationContext().getResources().getConfiguration().fontScale;
+  }
+
+  @Override
+  public String getName() {
+    return "DeviceInfo";
+  }
+
+  @Override
+  public @Nullable Map<String, Object> getConstants() {
+    HashMap<String, Object> constants = new HashMap<>();
+    constants.put(
+        "Dimensions",
+        getDimensionsConstants());
+    return constants;
+  }
+
+  @Override
+  public void onHostResume() {
+    float fontScale = getReactApplicationContext().getResources().getConfiguration().fontScale;
+    if (mFontScale != fontScale) {
+      mFontScale = fontScale;
+      emitUpdateDimensionsEvent();
+    }
+  }
+
+  @Override
+  public void onHostPause() {
+  }
+
+  @Override
+  public void onHostDestroy() {
+  }
+
+  public void emitUpdateDimensionsEvent() {
+    getReactApplicationContext()
+        .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
+        .emit("didUpdateDimensions", getDimensionsConstants());
+  }
+
+  private WritableMap getDimensionsConstants() {
+    DisplayMetrics windowDisplayMetrics = DisplayMetricsHolder.getWindowDisplayMetrics();
+    DisplayMetrics screenDisplayMetrics = DisplayMetricsHolder.getScreenDisplayMetrics();
+
+    WritableMap windowDisplayMetricsMap = Arguments.createMap();
+    windowDisplayMetricsMap.putInt("width", windowDisplayMetrics.widthPixels);
+    windowDisplayMetricsMap.putInt("height", windowDisplayMetrics.heightPixels);
+    windowDisplayMetricsMap.putDouble("scale", windowDisplayMetrics.density);
+    windowDisplayMetricsMap.putDouble("fontScale", mFontScale);
+    windowDisplayMetricsMap.putDouble("densityDpi", windowDisplayMetrics.densityDpi);
+
+    WritableMap screenDisplayMetricsMap = Arguments.createMap();
+    screenDisplayMetricsMap.putInt("width", screenDisplayMetrics.widthPixels);
+    screenDisplayMetricsMap.putInt("height", screenDisplayMetrics.heightPixels);
+    screenDisplayMetricsMap.putDouble("scale", screenDisplayMetrics.density);
+    screenDisplayMetricsMap.putDouble("fontScale", mFontScale);
+    screenDisplayMetricsMap.putDouble("densityDpi", screenDisplayMetrics.densityDpi);
+
+    WritableMap dimensionsMap = Arguments.createMap();
+    dimensionsMap.putMap("windowPhysicalPixels", windowDisplayMetricsMap);
+    dimensionsMap.putMap("screenPhysicalPixels", screenDisplayMetricsMap);
+
+    return dimensionsMap;
+  }
+}