Android: Speed up kitkat test listing for instrumentation tests

When enumerating classes, filter out those that do not have
"Test" suffix.

Spot checked 2 random shards of android-kitkat-arm-rel with and
without this change. Both before shards took 41 seconds to list
tests. Both after shards took 23 seconds.

Change-Id: I35b5521095a9ccea857b8fed6d9d009a7d9c7c7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946432
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720659}

base/test/android/javatests/src/org/chromium/base/test/BaseChromiumAndroidJUnitRunner.java

@@ -346,6 +346,15 @@ public class BaseChromiumAndroidJUnitRunner extends AndroidJUnitRunner {
                     if (startsWithAny(className, mExcludedPrefixes)) {
                         continue;
                     }
+                    if (!className.endsWith("Test")) {
+                        // Speeds up test listing to filter by name before
+                        // trying to load the class. We have an ErrorProne
+                        // check that enforces this convention:
+                        // //tools/android/errorprone_plugin/src/org/chromium/tools/errorprone/plugin/TestClassNameCheck.java
+                        // As of Dec 2019, this speeds up test listing on
+                        // android-kitkat-arm-rel from 41s -> 23s.
+                        continue;
+                    }
                     if (!className.contains("$") && loader.loadIfTest(className) != null) {
                         addTestClass(className);
                     }