weblayer: Add onBackgroundColorChanged

Bug: 1076473
Change-Id: I2c5de6c967dca2b2efe536c04d383e1d51c05ac1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264256
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781954}

weblayer/browser/android/javatests/src/org/chromium/weblayer/test/TabCallbackTest.java

@@ -321,4 +321,33 @@ public class TabCallbackTest {
         Assert.assertEquals("foobar", titles[0]);
         CriteriaHelper.pollUiThread(() -> Criteria.checkThat(titles[0], Matchers.is("foobar")));
     }
+
+    @MinWebLayerVersion(85)
+    @Test
+    @SmallTest
+    public void testOnBackgroundColorChanged() throws TimeoutException {
+        String startupUrl = "about:blank";
+        InstrumentationActivity activity = mActivityTestRule.launchShellWithUrl(startupUrl);
+
+        Integer backgroundColors[] = new Integer[1];
+        CallbackHelper callbackHelper = new CallbackHelper();
+        TestThreadUtils.runOnUiThreadBlocking(() -> {
+            Tab tab = activity.getTab();
+            TabCallback callback = new TabCallback() {
+                @Override
+                public void onBackgroundColorChanged(int color) {
+                    backgroundColors[0] = color;
+                    callbackHelper.notifyCalled();
+                }
+            };
+            tab.registerTabCallback(callback);
+        });
+
+        mActivityTestRule.executeScriptSync(
+                "document.body.style.backgroundColor = \"rgb(255, 0, 0)\"",
+                /*useSeparateIsolate=*/false);
+
+        callbackHelper.waitForFirst();
+        Assert.assertEquals(0xffff0000, (int) backgroundColors[0]);
+    }
 }

weblayer/browser/java/org/chromium/weblayer_private/TabImpl.java

@@ -170,6 +170,17 @@ public final class TabImpl extends ITab.Stub implements LoginPrompt.Observer {
                 viewController.onBottomControlsChanged(bottomControlsOffsetY);
             }
         }
+
+        @Override
+        public void onBackgroundColorChanged(int color) {
+            if (WebLayerFactoryImpl.getClientMajorVersion() >= 85) {
+                try {
+                    mClient.onBackgroundColorChanged(color);
+                } catch (RemoteException e) {
+                    throw new APICallException(e);
+                }
+            }
+        }
     }
 
     public static TabImpl fromWebContents(WebContents webContents) {

weblayer/browser/java/org/chromium/weblayer_private/interfaces/ITabClient.aidl

@@ -36,4 +36,7 @@ interface ITabClient {
 
   // Added in M84.
   void onTabDestroyed() = 8;
+
+  // Added in M85.
+  void onBackgroundColorChanged(in int color) = 9;
 }

weblayer/public/java/org/chromium/weblayer/Tab.java

@@ -726,6 +726,14 @@ public class Tab {
                 callback.bringTabToFront();
             }
         }
+
+        @Override
+        public void onBackgroundColorChanged(int color) {
+            StrictModeWorkaround.apply();
+            for (TabCallback callback : mCallbacks) {
+                callback.onBackgroundColorChanged(color);
+            }
+        }
     }
 
     private static final class ErrorPageCallbackClientImpl extends IErrorPageCallbackClient.Stub {

weblayer/public/java/org/chromium/weblayer/TabCallback.java

@@ -54,4 +54,14 @@ public abstract class TabCallback {
      * containing Activity, and the task to be foregrounded.
      */
     public void bringTabToFront() {}
+
+    /**
+     * Called when then background color of the page changes. The background color typically comes
+     * from css background-color, but heuristics and blending may be used depending upon the page.
+     * This is mostly useful for filling in gaps around the web page during resize, but it will
+     * not necessarily match the full background of the page.
+     * @param color The new ARGB color of the page background.
+     * @since 85
+     */
+    public void onBackgroundColorChanged(int color) {}
 }