Change the test tab load observer to print a clearer error message.

chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java

Index: chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java
diff --git a/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java b/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java
index ca1b0429fc2e8566128f93a97e8e1a1fd5dc0006..3b0be216af4c3269b1d4f5c85594b3a0e71ea231 100644
--- a/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java
+++ b/chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/TabLoadObserver.java
@@ -6,16 +6,22 @@ package org.chromium.chrome.test.util.browser;
 
 import android.text.TextUtils;
 
+import junit.framework.Assert;
+
 import org.chromium.base.ThreadUtils;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.content.browser.test.util.Criteria;
+import org.chromium.content.browser.test.util.CriteriaHelper;
 import org.chromium.content_public.browser.LoadUrlParams;
 
+import java.util.Locale;
+import java.util.concurrent.atomic.AtomicReference;
+
 /**
  * Monitors that a Tab starts loading and stops loading a URL.
  */
-public class TabLoadObserver extends EmptyTabObserver implements Criteria {
+public class TabLoadObserver extends EmptyTabObserver {
     private static final float FLOAT_EPSILON = 0.001f;
 
     private final Tab mTab;
@@ -53,21 +59,68 @@ public class TabLoadObserver extends EmptyTabObserver implements Criteria {
         mTabLoadStopped = true;
     }
 
-    @Override
-    public boolean isSatisfied() {
-        if (!mTabLoadStarted) return false;
-        if (!mTabLoadStopped) return false;
-        if (!mTab.isLoadingAndRenderingDone()) return false;
+    /**
+     * Asserts the page has loaded.
+     * @param maxAllowedTime The maximum time this will wait for the page to load.
+     */
+    public void assertLoaded(long maxAllowedTime) throws InterruptedException {
+        final AtomicReference<String> failureReason = new AtomicReference<>();
 
-        if (mExpectedTitle != null && !TextUtils.equals(mExpectedTitle, mTab.getTitle())) {
-            return false;
-        }
-        if (mExpectedScale != null) {
-            if (mTab.getContentViewCore() == null) return false;
-            if (Math.abs(mExpectedScale - mTab.getContentViewCore().getScale()) >= FLOAT_EPSILON) {
-                return false;
+        Criteria loadedCriteria = new Criteria() {
+            @Override
+            public boolean isSatisfied() {
+                if (!mTabLoadStarted) {
+                    failureReason.set("load started never called");
+                    return false;
+                }
+                if (!mTabLoadStopped) {
+                    failureReason.set("load stopped never called");
+                    return false;
+                }
+                if (!mTab.isLoadingAndRenderingDone()) {
+                    failureReason.set("load and rendering never completed");
+                    return false;
+                }
+
+                String title = mTab.getTitle();
+                if (mExpectedTitle != null && !TextUtils.equals(mExpectedTitle, title)) {
+                    failureReason.set(String.format(
+                            Locale.ENGLISH,
+                            "title did not match -- expected: \"%s\", actual \"%s\"",
+                            mExpectedTitle, title));
+                    return false;
+                }
+                if (mExpectedScale != null) {
+                    if (mTab.getContentViewCore() == null) {
+                        failureReason.set("tab has no content view core");
+                        return false;
+                    }
+
+                    float scale = mTab.getContentViewCore().getScale();
+                    if (Math.abs(mExpectedScale - scale) >= FLOAT_EPSILON) {
+                        failureReason.set(String.format(
+                                Locale.ENGLISH,
+                                "scale did not match with allowed epsilon -- "
+                                + "expected: \"%f\", actual \"%f\"", mExpectedScale, scale));
+                        return false;
+                    }
+                }
+                failureReason.set(null);
+                return true;
             }
+        };
+
+        boolean result = CriteriaHelper.pollForUIThreadCriteria(
+                loadedCriteria, maxAllowedTime, CriteriaHelper.DEFAULT_POLLING_INTERVAL);
+        if (!result) {
+            Assert.fail("Tab not fully loaded because: " + failureReason.get());
         }
-        return true;
+    }
+
+    /**
+     * Asserts that the page has loaded.
+     */
+    public void assertLoaded() throws InterruptedException {
+        assertLoaded(CriteriaHelper.DEFAULT_MAX_TIME_TO_POLL);
     }
 }