Add "panel_fitting" GPU feature type and use it for mirror mode.

content/browser/gpu/gpu_util_unittest.cc

Index: content/browser/gpu/gpu_util_unittest.cc
diff --git a/content/browser/gpu/gpu_util_unittest.cc b/content/browser/gpu/gpu_util_unittest.cc
index b92b5f81017bf2bf9978c10f47546fff107f7c3a..5179dfe50b18abe98681ef0389d2de656f5f8ff5 100644
--- a/content/browser/gpu/gpu_util_unittest.cc
+++ b/content/browser/gpu/gpu_util_unittest.cc
@@ -25,6 +25,8 @@ TEST(GpuUtilsTest, GpuFeatureTypFromString) {
             content::GPU_FEATURE_TYPE_TEXTURE_SHARING);
   EXPECT_EQ(gpu_util::StringToGpuFeatureType("accelerated_video_decode"),
             content::GPU_FEATURE_TYPE_ACCELERATED_VIDEO_DECODE);
+  EXPECT_EQ(gpu_util::StringToGpuFeatureType("panel_fitting"),
+            content::GPU_FEATURE_TYPE_PANEL_FITTING);
   EXPECT_EQ(gpu_util::StringToGpuFeatureType("all"),
             content::GPU_FEATURE_TYPE_ALL);
   EXPECT_EQ(gpu_util::StringToGpuFeatureType("xxx"),
@@ -67,6 +69,10 @@ TEST(GpuUtilsTest, GpuFeatureTypeToString) {
       "accelerated_video_decode");
   EXPECT_STREQ(
       gpu_util::GpuFeatureTypeToString(
+          content::GPU_FEATURE_TYPE_PANEL_FITTING).c_str(),
+      "panel_fitting");
+  EXPECT_STREQ(
+      gpu_util::GpuFeatureTypeToString(
           content::GPU_FEATURE_TYPE_ALL).c_str(),
       "all");
   EXPECT_STREQ(gpu_util::GpuFeatureTypeToString(