Make WebView work for external displays (over Presentations).

ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java

Index: ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java
diff --git a/ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java b/ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java
index da8e0262a1f9e202086b5d4095cc61b47555dd48..e365c94f150bf1ae30e1789418d2e78905975a0b 100644
--- a/ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java
+++ b/ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java
@@ -17,6 +17,8 @@ import android.view.WindowManager;
 import org.chromium.base.CalledByNative;
 import org.chromium.base.JNINamespace;
 
+import java.lang.ref.WeakReference;
+
 /**
  * This class facilitates access to android information typically only
  * available using the Java SDK, including {@link Display} properties.
@@ -27,14 +29,17 @@ import org.chromium.base.JNINamespace;
 @JNINamespace("gfx")
 public class DeviceDisplayInfo {
 
-    private final Context mAppContext;
+    private final WeakReference<Context> mContextRef;
     private final WindowManager mWinManager;
     private Point mTempPoint = new Point();
     private DisplayMetrics mTempMetrics = new DisplayMetrics();
 
-    private DeviceDisplayInfo(Context context) {
-        mAppContext = context.getApplicationContext();
-        mWinManager = (WindowManager) mAppContext.getSystemService(Context.WINDOW_SERVICE);
+    private DeviceDisplayInfo(WeakReference<Context> contextRef) {
+        mContextRef = contextRef;
+        Context context = mContextRef.get();
+        if (context == null)
+            throw new RuntimeException("got null Context in DeviceDisplayInfo constructor");
+        mWinManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
     }
 
     /**
@@ -154,7 +159,10 @@ public class DeviceDisplayInfo {
      */
     @CalledByNative
     private int getSmallestDIPWidth() {
-        return mAppContext.getResources().getConfiguration().smallestScreenWidthDp;
+        Context context = mContextRef.get();
+        if (context == null)
+            throw new RuntimeException("null context in getSmallestDIPWidth!!!");
+        return context.getResources().getConfiguration().smallestScreenWidthDp;
     }
 
     /**
@@ -181,18 +189,6 @@ public class DeviceDisplayInfo {
         return 0;
     }
 
-    /**
-     * Inform the native implementation to update its cached representation of
-     * the DeviceDisplayInfo values.
-     */
-    public void updateNativeSharedDisplayInfo() {
-        nativeUpdateSharedDeviceDisplayInfo(
-                getDisplayHeight(), getDisplayWidth(),
-                getPhysicalDisplayHeight(), getPhysicalDisplayWidth(),
-                getBitsPerPixel(), getBitsPerComponent(),
-                getDIPScale(), getSmallestDIPWidth(), getRotationDegrees());
-    }
-
     private Display getDisplay() {
         return mWinManager.getDefaultDisplay();

[jdduke (slow), 2015/06/16 15:01:28]

So the "default" Display can vary per WindowManager, and the WindowManager can
very between activities? Is that how this works?

[gsennton, 2015/06/17 11:40:36]

AFAICT this is indeed the case, e.g. using WebView with a Presentation
http://developer.android.com/reference/android/app/Presentation.html and using
the window manager of the current activity context here gives us the display
targeted by the Presentation (while using the application context instead gives
us the primary display).

[gsennton, 2015/06/25 13:59:58]

I should clarify this (my comment above is not entirely correct):
As described in
https://cs.corp.google.com/#android/frameworks/base/core/java/android/view/Wi...
a WindowManager is connected/bound to a certain display.
What a Presentation does is create its own context using
Context#createDisplayContext to target a certain Display. That context is
different from the application context and also different from the context of
the activity containing the Presentation. That is why we need to use the context
passed to WebView rather than its application context to fetch the metrics of
the targeted display.

I am not sure how this will work with ActivityWindowAndroid since the
Presentation context is not necessarily an activity context.

     }
@@ -205,13 +201,6 @@ public class DeviceDisplayInfo {
      */
     @CalledByNative
     public static DeviceDisplayInfo create(Context context) {
-        return new DeviceDisplayInfo(context);
+        return new DeviceDisplayInfo(new WeakReference<Context>(context));
     }
-
-    private native void nativeUpdateSharedDeviceDisplayInfo(
-            int displayHeight, int displayWidth,
-            int physicalDisplayHeight, int physicalDisplayWidth,
-            int bitsPerPixel, int bitsPerComponent, double dipScale,
-            int smallestDIPWidth, int rotationDegrees);
-
 }