Migrate from android::String isEmpty to empty

This empty method is different from the old one - it aligns with
std::string definition.

Bug: 295394788
Test: make checkbuild
Change-Id: Id74502de0e51182aa9629db8dc70739be4483d12
Merged-In: Id74502de0e51182aa9629db8dc70739be4483d12
diff --git a/libs/gui/tests/GLTest.cpp b/libs/gui/tests/GLTest.cpp
index 73e8fbe..449cbf9 100644
--- a/libs/gui/tests/GLTest.cpp
+++ b/libs/gui/tests/GLTest.cpp
@@ -191,24 +191,24 @@
         msg += String8::format("r(%d isn't %d)", pixel[0], r);
     }
     if (g >= 0 && abs(g - int(pixel[1])) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("g(%d isn't %d)", pixel[1], g);
     }
     if (b >= 0 && abs(b - int(pixel[2])) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("b(%d isn't %d)", pixel[2], b);
     }
     if (a >= 0 && abs(a - int(pixel[3])) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("a(%d isn't %d)", pixel[3], a);
     }
-    if (!msg.isEmpty()) {
+    if (!msg.empty()) {
         return ::testing::AssertionFailure(::testing::Message(msg.c_str()));
     } else {
         return ::testing::AssertionSuccess();
@@ -223,24 +223,24 @@
         msg += String8::format("left(%d isn't %d)", r1.left, r2.left);
     }
     if (abs(r1.top - r2.top) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("top(%d isn't %d)", r1.top, r2.top);
     }
     if (abs(r1.right - r2.right) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("right(%d isn't %d)", r1.right, r2.right);
     }
     if (abs(r1.bottom - r2.bottom) > tolerance) {
-        if (!msg.isEmpty()) {
+        if (!msg.empty()) {
             msg += " ";
         }
         msg += String8::format("bottom(%d isn't %d)", r1.bottom, r2.bottom);
     }
-    if (!msg.isEmpty()) {
+    if (!msg.empty()) {
         msg += String8::format(" R1: [%d %d %d %d] R2: [%d %d %d %d]",
                                r1.left, r1.top, r1.right, r1.bottom,
                                r2.left, r2.top, r2.right, r2.bottom);