[AW] lookup resource id in AndroidProtocolHandler using getIdentifier

Use android.content.res.Resources#getIdentifier to lookup app resource
id and fall back to class look up by reflection if it fails. Looking up
resources this way may help fixing this long standing bug b/37102241.

This also record a boolean histogram to track lookup success and
failure.

Bug: 923956, b/37102241
Test: Build an app with gradle and applicationId and test load a resource file in WebView
Change-Id: Id42935b763f52572e184ba8564eb95f38df63171
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288556
Commit-Queue: Hazem Ashmawy <hazems@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787495}

android_webview/java/src/org/chromium/android_webview/AndroidProtocolHandler.java

@@ -4,6 +4,7 @@
 
 package org.chromium.android_webview;
 
+import android.content.Context;
 import android.content.res.AssetManager;
 import android.net.Uri;
 import android.util.Log;
@@ -13,6 +14,7 @@
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 import org.chromium.base.annotations.NativeMethods;
+import org.chromium.base.metrics.RecordHistogram;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -93,8 +95,18 @@ private static Class<?> getClazz(String packageName, String assetType)
 
     private static int getFieldId(String assetType, String assetName)
             throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
+        Context appContext = ContextUtils.getApplicationContext();
+        String packageName = appContext.getPackageName();
+        int id = appContext.getResources().getIdentifier(assetName, assetType, packageName);
+        if (id != 0) {
+            RecordHistogram.recordBooleanHistogram(
+                    "Android.WebView.AndroidProtocolHandler.ResourceGetIdentifier", true);
+            return id;
+        }
+        // Resource id can't be found using Resources class so fallback to reflection.
+        // TODO(https://crbug.com/923956) remove reflection fallback if the histogram is always
+        // true.
         Class<?> clazz = null;
-        String packageName = ContextUtils.getApplicationContext().getPackageName();
         try {
             clazz = getClazz(packageName, assetType);
         } catch (ClassNotFoundException e) {
@@ -111,9 +123,10 @@ private static int getFieldId(String assetType, String assetName)
                 }
             }
         }
-
+        RecordHistogram.recordBooleanHistogram(
+                "Android.WebView.AndroidProtocolHandler.ResourceGetIdentifier", false);
         java.lang.reflect.Field field = clazz.getField(assetName);
-        int id = field.getInt(null);
+        id = field.getInt(null);
         return id;
     }
 

tools/metrics/histograms/histograms.xml

@@ -4976,6 +4976,17 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Android.WebView.AndroidProtocolHandler.ResourceGetIdentifier"
+    enum="BooleanSuccess" expires_after="2021-01-30">
+  <owner>hazems@chromium.org</owner>
+  <owner>src/android_webview/OWNERS</owner>
+  <summary>
+    Track if looking up Android app resource id using
+    android.content.res.Resources#getIdentifier succeeds in
+    AndroidProtocolHandler or if it falls back to reflection look up.
+  </summary>
+</histogram>
+
 <histogram name="Android.WebView.AndroidX.ApiCall" enum="AndroidXWebkitApiCall"
     expires_after="2021-01-29">
   <owner>laisminchillo@chromium.org</owner>