When possible, draw the toolbar shadow with the compositor

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 4218cb93449848983c5275b0fe65a4a2e22a6a4d..ec0520e7199142c2bb8782d70ee4cc5dd8851242 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
@@ -354,6 +354,14 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         mCompositorViewHolder = (CompositorViewHolder) findViewById(R.id.compositor_view_holder);
         mCompositorViewHolder.setRootView(rootView);
 
+        mCompositorViewHolder.setFrameObserver(new CompositorViewHolder.FrameObserver() {
+            @Override
+            public void onCompositorFrame() {
+                if (mToolbarManager == null) return;
+                mToolbarManager.onFirstCompositorFrame();
+            }
+        });
+
         // Setting fitsSystemWindows to false ensures that the root view doesn't consume the insets.
         rootView.setFitsSystemWindows(false);