Delegate horizontal scrolls from the Hotseat to the Workspace

=> Before this change, scrolling horizontally on the the hotseat area was a no-op
=> This is a mild usability issue (or arguably WAI) for the default grid, but for larger grids it feels really broken as you have to reach very high just to scroll to another page.

issue 156507399

Test: manual. Also verified that swipe up still works and goes through the same code path.

Change-Id: I760aca473dd36bc8cfb906cb58e897e2ab7fd1d9

src/com/android/launcher3/Hotseat.java

@@ -38,6 +38,8 @@ public class Hotseat extends CellLayout implements LogContainerProvider, Insetta
 
     @ViewDebug.ExportedProperty(category = "launcher")
     private boolean mHasVerticalHotseat;
+    private Workspace mWorkspace;
+    private boolean mSendTouchToWorkspace;
 
     public Hotseat(Context context) {
         this(context, null);
@@ -112,8 +114,35 @@ public class Hotseat extends CellLayout implements LogContainerProvider, Insetta
         InsettableFrameLayout.dispatchInsets(this, insets);
     }
 
+    public void setWorkspace(Workspace w) {
+        mWorkspace = w;
+    }
+
+    @Override
+    public boolean onInterceptTouchEvent(MotionEvent ev) {
+        // We allow horizontal workspace scrolling from within the Hotseat. We do this by delegating
+        // touch intercept the Workspace, and if it intercepts, delegating touch to the Workspace
+        // for the remainder of the this input stream.
+        int yThreshold = getMeasuredHeight() - getPaddingBottom();
+        if (mWorkspace != null && ev.getY() <= yThreshold) {
+            mSendTouchToWorkspace = mWorkspace.onInterceptTouchEvent(ev);
+            return mSendTouchToWorkspace;
+        }
+        return false;
+    }
+
     @Override
     public boolean onTouchEvent(MotionEvent event) {
+        // See comment in #onInterceptTouchEvent
+        if (mSendTouchToWorkspace) {
+            final int action = event.getAction();
+            switch (action & MotionEvent.ACTION_MASK) {
+                case MotionEvent.ACTION_UP:
+                case MotionEvent.ACTION_CANCEL:
+                    mSendTouchToWorkspace = false;
+            }
+            return mWorkspace.onTouchEvent(event);
+        }
         return event.getY() > getCellHeight();
     }
 }

src/com/android/launcher3/Launcher.java

@@ -1116,6 +1116,7 @@ public class Launcher extends StatefulActivity<LauncherState> implements Launche
         mWorkspace.initParentViews(mDragLayer);
         mOverviewPanel = findViewById(R.id.overview_panel);
         mHotseat = findViewById(R.id.hotseat);
+        mHotseat.setWorkspace(mWorkspace);
 
         mLauncherView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                 | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION