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..15ba5809f9299be9c7381e055737bbaa4e514fe7 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.
@@ -26,15 +28,17 @@ 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)

[boliu, 2015/07/15 06:38:47]

Pass a strong ref in constructor, then this can't ever happen

[gsennton, 2015/07/15 19:26:21]

Unless the incoming context is null because we retrieved it from WindowAndroid
which only holds a weak reference to its display context (and therefore might
pass null)?

[boliu, 2015/07/16 14:36:56]

You can check for null before passing it into DeviceDisplayInfo then. And if it
is null, you'll have to handle that correctly too. Make a dummy
DeviceDisplayInfo, or check caller can handle null?

[gsennton, 2015/10/20 13:27:12]

Right, will check this in WindowAndroid::UpdateDeviceDisplayInfo and just use
the default DeviceDisplayInfo ctor if the context is null.

[boliu, 2015/10/20 15:07:22]

"use the default DeviceDisplayInfo" sounds wrong, but then maybe it doesn't
matter much since this can only be null momentarily during shutdown. So add a
comment if you decide to do that.

+            throw new RuntimeException("got null Context in DeviceDisplayInfo constructor");
+        mWinManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
     }
 
     /**
@@ -154,7 +158,9 @@ 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;

[boliu, 2015/07/15 06:38:47]

I wonder if this can ever change. Maybe it's ok to cache the value in the
constructor.

Throwing exception is not ok. That's the same as crashing in a @CalledByNative
method, and an object going away under a weak pointer has to be handled without
crashing.

[jdduke (slow), 2015/07/15 16:03:07]

+1. It might also be worth investigating why this constant is needed, and if
it's absolutely necessary. Regardless, even if the value does change I don't
think we'd react to the change properly anyway, and I'd be OK storing it in the
constructor.

[gsennton, 2015/07/15 19:26:21]

Right, going ahead and storing the value in the constructor.

Checking with skobes@ whether getSmallestDIPWidth can be removed
(it was added in https://codereview.chromium.org/28053002).

[boliu, 2015/07/16 14:36:56]

You no longer need to keep mContextRef in this class then \o/

[gsennton, 2015/10/20 13:27:12]

will remove mContextRef

Regarding getSmallestDIPWidth, according to skobes@ the value is needed but can
probably be calculated in the following way

int smallestDIPWidth = min(info.GetPhysicalDisplayHeight(),
info.GetPhysicalDisplayWidth()) / info.GetDIPScale();

     }
 
     /**
@@ -181,18 +187,6 @@ 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();
     }
@@ -205,13 +199,6 @@ 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);
-
 }