Make WebView work for external displays (over Presentations).

content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java

Index: content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
index 929e494039c791499ebb359716cf9526ab8b12d8..da3c9480df1091bbb5914156ef73c833a237ae86 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
@@ -601,6 +601,9 @@ public class ContentViewCore implements
     // The client that implements Contextual Search functionality, or null if none exists.
     private ContextualSearchClient mContextualSearchClient;
 
+    // Listener for screen orientation changes.
+    private ScreenOrientationListener mScreenOrientationListener;

[boliu, 2015/07/15 06:38:46]

This should be per context, instead of per contentviewcore

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

I don't quite understand this, aren't we only holding one context in
contentviewcore anyway? (and how do you mean this would look if it was per
context?)

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

Many ContentViewCore can have the same context, in which case they should share
the same ScreenOrientationListener.

One hacky way to implement it is keep a static WeakHashMap<Context,
ScreenOrientationListener>. Cleaner concept would be to move
ScreenOrientationListener entirely into WindowAndroid.

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

Is there any way for us to guarantee that we can call
ScreenOrientationListener.removeObserver from WindowAndroid? E.g. can we do it
in WindowAndroid.destroy()? In ContentViewCore we do it not only in destroy()
but also in OnDetachedFromWindow to make sure it is always called.


AFAICT some (if not all) of the changes I have proposed to
ScreenOrientationListener might not be needed because of the way we listen for
display updates --
The first way we do it is to call Context.registerComponentCallbacks which for
Context.java runs getApplicationContext().registerComponentCallbacks(), see 
https://cs.corp.google.com/#android/frameworks/base/core/java/android/content...
(though Application.java overrides this method to customize this).
The second way is to get the DisplayManager for the context and call
registerDisplayListener on it:
https://cs.corp.google.com/#android/frameworks/base/core/java/android/hardwar...
(and that function is implemented through register listeners to a global
DisplayManager which should be the same for all different Contexts).
So if this won't change in the future we could store application contexts in
ScreenOrientationListener (rather than weak references to display/activity
contexts) and thus we would be able unregister our listeners even when our
weakly referenced contexts have been destructed. Does this seem ok? (I am unsure
about relying on the internal implementation of Android here).

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

Those don't have to move? Change

ScreenOrientationListener.getInstance().removeObserver(this);

to

mWindowAndroid.getScreenOrientationListener().removeObserve(this);

or something like that?
Interesting. So android has no way to observer orientation change of the
external display in any way? Interesting...

However, that just mean CVC connected to an external window should *not*
observer any orientation change events? No idea how to actually implement that
though :/

[gsennton, 2015/10/20 18:46:44]

Ah, we could have the WindowAndroids be ScreenOrientationObservers and just add
them through calling
mScreenOrientationListener().addObserver(mWindowAndroid) ....
then if we would happen to add the same WindowAndroid several times we would
just hit
https://code.google.com/p/chromium/codesearch#chromium/src/content/public/and...
and thus not add the observer unnecessarily.
If I interpret this correctly there was no way to observe orientation changes of
external displays before android version 17 because that is when DisplayManager
and Presentation were added.
The callback we use from DisplayManager looks like this:

void onDisplayChanged(int displayId);

so it should support different displays.

[boliu, 2015/10/21 15:54:59]

The issue to be careful with supporting adding he same observer multiple times
is you have to support removing the observer multiple times too. I recommend
solving this in WindowAndroid, not the observer pattern.
Hmm, that implies orientation observer need to be re-implemented using
DisplayManager.DisplayListener instead to do this? Webivew only need to run on
21 and up, but chrome still supports back to 16 I think. So need to write in a
way that gracefully fall back to old implementation on older devices.

[gsennton, 2015/10/21 16:35:32]

Right, the removal is problematic...


We already use DisplayListener in ScreenOrientationListener :). Or do you mean
that we should use it in some other way?

+
     /**
      * @param webContents The {@link WebContents} to find a {@link ContentViewCore} of.
      * @return            A {@link ContentViewCore} that is connected to {@code webContents} or
@@ -639,6 +642,7 @@ public class ContentViewCore implements
         mEditable = Editable.Factory.getInstance().newEditable("");
         Selection.setSelection(mEditable, 0);
         mContainerViewObservers = new ObserverList<ContainerViewObserver>();
+        mScreenOrientationListener = new ScreenOrientationListener(mContext);
     }
 
     /**
@@ -1002,7 +1006,7 @@ public class ContentViewCore implements
         mRetainedJavaScriptObjects.clear();
         unregisterAccessibilityContentObserver();
         mGestureStateListeners.clear();
-        ScreenOrientationListener.getInstance().removeObserver(this);
+        mScreenOrientationListener.removeObserver(this);
         mPositionObserver.clearListener();
         mContainerViewObservers.clear();
 
@@ -1493,7 +1497,7 @@ public class ContentViewCore implements
         setAccessibilityState(mAccessibilityManager.isEnabled());
         setTextHandlesTemporarilyHidden(false);
         restoreSelectionPopupsIfNecessary();
-        ScreenOrientationListener.getInstance().addObserver(this, mContext);
+        mScreenOrientationListener.addObserver(this);
         GamepadList.onAttachedToWindow(mContext);
         mAccessibilityManager.addAccessibilityStateChangeListener(this);
         mSystemCaptioningBridge.addListener(this);
@@ -1508,7 +1512,7 @@ public class ContentViewCore implements
         mZoomControlsDelegate.dismissZoomPicker();
         unregisterAccessibilityContentObserver();
 
-        ScreenOrientationListener.getInstance().removeObserver(this);
+        mScreenOrientationListener.removeObserver(this);
         GamepadList.onDetachedFromWindow();
         mAccessibilityManager.removeAccessibilityStateChangeListener(this);