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Example error from logs:

===Running apply_issue.bat --root_dir src --issue 807853003 --server https://codereview.chromium.org --force --ignore_deps -v -v --no-auth --patchset 120001 --blacklist DEPS (attempt #1)===
In directory: E:\b\build\slave\win\build
Connecting to https://codereview.chromium.org
DEBUG    rietveld( 402): POSTing to /api/807853003, args {'payload': None, 'timeout': 15}.
DEBUG    rietveld( 419): /api/807853003
DEBUG    rietveld( 402): POSTing to /807853003/patchset/120001/get_depends_on_patchset, args {'timeout': 15, 'payload': '---M-A-G-I-C---B-O-U-N-D-A-R-Y-0---\r\n', 'content_type': 'multipart/form-data; boundary=-M-A-G-I-C---B-O-U-N-D-A-R-Y-0-'}.
DEBUG    rietveld( 419): /807853003/patchset/120001/get_depends_on_patchset
Downloading patch from https://codereview.chromium.org/807853003/#ps120001
DEBUG    rietveld( 402): POSTing to /api/807853003/120001, args {'payload': None, 'timeout': 15}.
DEBUG    rietveld( 419): /api/807853003/120001
DEBUG    rietveld( 133): content/common/gpu/client/gl_helper_readback_support.cc
DEBUG    rietveld( 402): POSTing to /download/issue807853003_120001_130001.diff, args {'payload': None, 'timeout': 15}.
DEBUG    rietveld( 419): /download/issue807853003_120001_130001.diff
      content/common/gpu/client/gl_helper_readback_support.cc

Applying the patch from https://codereview.chromium.org/807853003/#ps120001
DEBUG subprocess2( 215): git apply --index -3 -p1 --verbose;  cwd=E:\b\build\slave\win\build\src
Failed to apply patch for content/common/gpu/client/gl_helper_readback_support.cc:
While running git apply --index -3 -p1 --verbose;
  Checking patch content/common/gpu/client/gl_helper_readback_support.cc...
  error: content/common/gpu/client/gl_helper_readback_support.cc: does not exist in index

Patch:       content/common/gpu/client/gl_helper_readback_support.cc
Index: content/common/gpu/client/gl_helper_readback_support.cc
diff --git a/content/common/gpu/client/gl_helper_readback_support.cc b/content/common/gpu/client/gl_helper_readback_support.cc
index e773ca90782a6dc684bec38c7afb455e1cfe925c..36fc825a79067fbd288b81c9c0fec8adec0f577d 100644
--- a/content/common/gpu/client/gl_helper_readback_support.cc
+++ b/content/common/gpu/client/gl_helper_readback_support.cc
@@ -25,8 +25,8 @@ void GLHelperReadbackSupport::InitializeReadbackSupport() {
   for (int i = 0; i <= kLastEnum_SkColorType; ++i) {
     format_support_table_[i] = GLHelperReadbackSupport::NOT_SUPPORTED;
   }
-  // TODO(sikugu): kAlpha_8_SkColorType support check is failing on mesa.
-  // See  crbug.com/415667 .
+
+  CheckForReadbackSupport(kAlpha_8_SkColorType);
   CheckForReadbackSupport(kRGB_565_SkColorType);
   CheckForReadbackSupport(kARGB_4444_SkColorType);
   CheckForReadbackSupport(kRGBA_8888_SkColorType);
@@ -38,6 +38,9 @@ void GLHelperReadbackSupport::CheckForReadbackSupport(
     SkColorType texture_format) {
   bool supports_format = false;
   switch (texture_format) {
+    case kAlpha_8_SkColorType:
+      supports_format = SupportsFormat(GL_ALPHA, GL_UNSIGNED_BYTE);
+      break;
     case kRGB_565_SkColorType:
       supports_format = SupportsFormat(GL_RGB, GL_UNSIGNED_SHORT_5_6_5);
       break;
@@ -135,6 +138,15 @@ GLHelperReadbackSupport::GetReadbackConfig(SkColorType color_type,
   *type = GL_UNSIGNED_BYTE;
   GLenum new_format = 0, new_type = 0;
   switch (color_type) {
+    case kAlpha_8_SkColorType:
+      if (format_support_table_[color_type] ==
+          GLHelperReadbackSupport::SUPPORTED) {
+        *format = GL_ALPHA;
+        *type = GL_UNSIGNED_BYTE;
+        *bytes_per_pixel = 1;
+        return GLHelperReadbackSupport::SUPPORTED;
+      }
+      break;
     case kRGB_565_SkColorType:
       if (format_support_table_[color_type] ==
           GLHelperReadbackSupport::SUPPORTED) {

CWD=E:\b\build\slave\win\build
Checkout path=E:\b\build\slave\win\build\src
===Failed in 0.1 mins===