Errorprone: enabling ModifyCollectionInEnhancedForLoop check

This also requires us to fix the one failing location.

Bug: 1029038
Change-Id: I85591b3c0d435d5ef9e725a8d27167aa266af3a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593837Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Auto-Submit: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837630}

android_webview/glue/java/src/com/android/webview/chromium/SplitApkWorkaround.java

@@ -14,6 +14,7 @@ import java.io.File;
 import java.lang.reflect.Array;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
+import java.util.ArrayList;
 import java.util.Map;
 
 /**
@@ -56,14 +57,16 @@ public class SplitApkWorkaround {
 
             // Synchronize on the map while trying to update it, as the framework does.
             synchronized (loaders) {
-                for (Map.Entry<String, ClassLoader> entry : loaders.entrySet()) {
+                // Copy of loaders keys, since we plan to modify loaders while iterating.
+                ArrayList<String> keys = new ArrayList(loaders.keySet());
+                for (String cacheKey : keys) {
                     try {
-                        if (!(entry.getValue() instanceof BaseDexClassLoader)) {
+                        ClassLoader value = loaders.get(cacheKey);
+                        if (!(value instanceof BaseDexClassLoader)) {
                             // If it's some other type it can't be the right one.
                             continue;
                         }
-                        String cacheKey = entry.getKey();
-                        BaseDexClassLoader cl = (BaseDexClassLoader) entry.getValue();
+                        BaseDexClassLoader cl = (BaseDexClassLoader) value;
 
                         // Get the list of files that this classloader uses as its classpath.
                         Object pathList = pathListField.get(cl);

build/android/gyp/compile_java.py

@@ -33,7 +33,6 @@ _JAVAC_EXTRACTOR = os.path.join(build_utils.DIR_SOURCE_ROOT, 'third_party',
 ERRORPRONE_WARNINGS_TO_DISABLE = [
     # These should really be turned on.
     'CollectionUndefinedEquality',
-    'ModifyCollectionInEnhancedForLoop',
     # The following are super useful, but existing issues need to be fixed first
     # before they can start failing the build on new errors.
     'InvalidParam',