Resize only the virtual viewport when the OSK triggers a resize.

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
index 162d1fa3d260bacf4d5b0edd52bc7e306bf99bb9..f1d9c094b4c3ad7e7225c4fa9d3250af981d6c40 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
@@ -205,6 +205,7 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
     private ActivityWindowAndroid mWindowAndroid;
     private ChromeFullscreenManager mFullscreenManager;
     private CompositorViewHolder mCompositorViewHolder;
+    private InsetConsumerView mInsetConsumerView;
     private ContextualSearchManager mContextualSearchManager;
     private ReaderModeManager mReaderModeManager;
     private SnackbarManager mSnackbarManager;
@@ -352,8 +353,20 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         // black status bar
         ApiCompatibilityUtils.setStatusBarColor(getWindow(), Color.BLACK);
 
+        ViewGroup rootView = (ViewGroup) getWindow().getDecorView().getRootView();
         mCompositorViewHolder = (CompositorViewHolder) findViewById(R.id.compositor_view_holder);
-        mCompositorViewHolder.setRootView(getWindow().getDecorView().getRootView());
+        mCompositorViewHolder.setRootView(rootView);
+
+        // Setting fitsSystemWindows to false ensures that the root view
+        // doesn't consume the insets.
+        rootView.setFitsSystemWindows(false);

[Ted C, 2016/03/14 22:53:06]

It would be nice to guard these lines with ChromeSwitches.ENABLE_OSK_OVERSCROLL
if it actually is only needed by them.

But that would require you hooking into initializeCompositor() instead of here
(that is the first call after native has been initialized).

Although you "could" get into a situation where the keyboard is already showing,
so you'd need to request requestFitSystemWindows().

More tried to isolate this if we want to roll it out as a unit.  Rolling this
out now will help us track down issues, so it might be worth it.

Also, you should try to get a multi-window supporting samsung phone or try out
with the new android n multi-window to make sure this logic is sane there.

[ymalik, 2016/03/15 16:23:26]

I like the idea of rolling the inset logic out now so we can track down issues.
Is it okay if I leave it here for now?
I tried the on Android M with multiwindow (enabled through developer settings)
and on Samsung Note 5.

On Android M with multiwindow, I found that the insets were not reported at all
(portrait and landscape mode; window stuck to top and bottom). It was as if the
keyboard just overlayed on top of the window. So this change doesn't really
affect multiwindow on Android M.

On Samsung Note 5, the behavior was interesting. The value of the insets
reported are truly the amount of screen obscured by the insets. 
Consider the following example to better explain the Samsung case:
Chrome is stuck to the top,
Height of the screen is X pixels, 
Chrome occupies y pixels before OSK,
App 2 occupies z pixels, where y + z = X and y > z
Height of the keyboard is w pixels, where w > z,
What chrome would see is w - z pixels of bottom insets. (Note that I didn't
actually measure this, but based on the numbers, this is what it seemed like.)

Similarly, when I put chrome on the bottom and the OSK showed up, it pushed the
window above the keyboard and reported the portion of the screen obscured by the
keyboard.

I think the way Samsung does it makes sense to me and we should do it the same
way. In any case, I would say that this change should't really break things.
WDYT? 

+
+        // Add a custom view right after the root view that stores the insets
+        // to access later. ContentViewCore needs the insets to determine the
+        // portion of the screen obscured by non-content displaying things
+        // such as the OSK.
+        mInsetConsumerView = InsetConsumerView.create(this);
+        rootView.addView(mInsetConsumerView, 0);
     }
 
     /**
@@ -1059,6 +1072,15 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         return mTabModelSelector;
     }
 
+    /**
+     * Returns the {@link InsetConsumerView} that has the current system window
+     * insets information.
+     * @return The {@link InsetConsumerView}, possibly null.
+     */
+    public InsetConsumerView getInsetConsumerView() {
+        return mInsetConsumerView;
+    }
+
     @Override
     public TabCreatorManager.TabCreator getTabCreator(boolean incognito) {
         return incognito ? mIncognitoTabCreator : mRegularTabCreator;