Make WebView work for external displays (over Presentations).

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

Index: ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
diff --git a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
index 27579e6e3ad4a3888f486f246f4f13e1c17e0c20..071b33fb29738e7b5252f9c265e32e153a94f32b 100644
--- a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
+++ b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
@@ -76,6 +76,12 @@ public class WindowAndroid {
 
     protected Context mApplicationContext;
     protected SparseArray<IntentCallback> mOutstandingIntents;
+    // For WebView to render properly on an external display through a Presentation we need to fetch

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

Avoid mentioning webview. This is needed in chrome too if one day it decides to
draw web contents in another display

+    // display metrics from the context provided by the Presentation.
+    // The display context differs from mApplicationContext in that mApplicationContext targets the
+    // primary display while the display context could target an external display (if WebView is
+    // shown in a Presentation).
+    protected WeakReference<Context> mDisplayContextRef;
 
     // Ideally, this would be a SparseArray<String>, but there's no easy way to store a
     // SparseArray<String> in a bundle during saveInstanceState(). So we use a HashMap and suppress
@@ -132,13 +138,13 @@ public class WindowAndroid {
      */
     @SuppressLint("UseSparseArrays")
     public WindowAndroid(Context context) {
-        assert context == context.getApplicationContext();
-        mApplicationContext = context;
+        mApplicationContext = context.getApplicationContext();

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

probably at a comment there that context may be the activity context, so can't
hold a strong ref to it from here

+        mDisplayContextRef = new WeakReference<Context>(context);
         mOutstandingIntents = new SparseArray<IntentCallback>();
         mIntentErrors = new HashMap<Integer, String>();
         mVSyncMonitor = new VSyncMonitor(context, mVSyncListener);
-        mAccessibilityManager = (AccessibilityManager)
-                context.getSystemService(Context.ACCESSIBILITY_SERVICE);
+        mAccessibilityManager = (AccessibilityManager) mApplicationContext.getSystemService(
+                Context.ACCESSIBILITY_SERVICE);
     }
 
     /**
@@ -562,6 +568,11 @@ public class WindowAndroid {
         });
     }
 
+    @CalledByNative
+    private Context getDisplayContext() {
+        return mDisplayContextRef.get();
+    }
+
     /**
      * Update whether the placeholder is 'drawn' based on whether an animation is running
      * or touch exploration is enabled - if either of those are true, we call