[aw] Throw exception for null String in findAllAsync

A null String shouldn't be passed to findAllAsync. This CL throws an
IllegalArgumentException so developers have an easier way debugging
(what would otherwise be a native crash).

Also add a new test in AwContentsTest.

Bug: 1014948
Change-Id: I7dd06dd4b09b3024c3f72ecbe3f227fec496fa25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1865172Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Laís Minchillo <laisminchillo@chromium.org>
Auto-Submit: Laís Minchillo <laisminchillo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707826}

android_webview/java/src/org/chromium/android_webview/AwContents.java

@@ -1623,9 +1623,11 @@ public class AwContents implements SmartClipProvider {
 
     public void findAllAsync(String searchString) {
         if (TRACE) Log.i(TAG, "%s findAllAsync", this);
-        if (!isDestroyed(WARN)) {
-            AwContentsJni.get().findAllAsync(mNativeAwContents, AwContents.this, searchString);
+        if (isDestroyed(WARN)) return;
+        if (searchString == null) {
+            throw new IllegalArgumentException("Search string shouldn't be null");
         }
+        AwContentsJni.get().findAllAsync(mNativeAwContents, AwContents.this, searchString);
     }
 
     public void findNext(boolean forward) {

android_webview/javatests/src/org/chromium/android_webview/test/AwContentsTest.java

@@ -1007,4 +1007,19 @@ public class AwContentsTest {
                 RecordHistogram.getHistogramValueCountForTesting(
                         AwContents.LOAD_URL_SCHEME_HISTOGRAM_NAME, expectedSchemeEnum));
     }
+
+    @Test
+    @Feature({"AndroidWebView"})
+    @SmallTest
+    public void testFindAllAsyncEmptySearchString() {
+        AwTestContainerView testView =
+                mActivityTestRule.createAwTestContainerViewOnMainSync(mContentsClient);
+        final AwContents awContents = testView.getAwContents();
+        try {
+            awContents.findAllAsync(null);
+            Assert.fail("A null searchString should cause an exception to be thrown");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+    }
 }