Android: use getDeclaredConstructor (errorprone warning)

No change to logic.

This uses getDeclaredConstructor to instantiate an instance for the
TestRunner. This propagates exceptions from the constructor, which means
we can log more error cases.

This resolves an errorprone compile warning (ClassNewInstance)

Test: ninja system_webview_apk (fewer warning messages)
Change-Id: I110b444ca93557d0ec138c2a05d8fda81904dfc8
Reviewed-on: https://chromium-review.googlesource.com/780808
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518395}

base/android/java/src/org/chromium/base/library_loader/Linker.java

@@ -458,7 +458,9 @@ public abstract class Linker {
             }
             TestRunner testRunner = null;
             try {
-                testRunner = (TestRunner) Class.forName(mTestRunnerClassName).newInstance();
+                testRunner = (TestRunner) Class.forName(mTestRunnerClassName)
+                                     .getDeclaredConstructor()
+                                     .newInstance();
             } catch (Exception e) {
                 Log.wtf(TAG, "Could not instantiate test runner class by name", e);
                 assertForTesting(false);