Implement GetTranslatedShaderSource in the passthrough cmd decoder.

Many WebGL tests use this function.

BUG=668223
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2532543002
Cr-Commit-Position: refs/heads/master@{#434877}

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc

@@ -2594,7 +2594,21 @@ error::Error GLES2DecoderPassthroughImpl::DoGetUniformsES3CHROMIUM(
 error::Error GLES2DecoderPassthroughImpl::DoGetTranslatedShaderSourceANGLE(
     GLuint shader,
     std::string* source) {
-  NOTIMPLEMENTED();
+  FlushErrors();
+  GLuint service_id = GetShaderServiceID(shader, resources_);
+  GLint translated_source_length = 0;
+  glGetShaderiv(service_id, GL_TRANSLATED_SHADER_SOURCE_LENGTH_ANGLE,
+                &translated_source_length);
+  if (FlushErrors()) {
+    return error::kNoError;
+  }
+
+  if (translated_source_length > 0) {
+    std::vector<char> buffer(translated_source_length, 0);
+    glGetTranslatedShaderSourceANGLE(service_id, translated_source_length,
+                                     nullptr, buffer.data());
+    *source = std::string(buffer.data());
+  }
   return error::kNoError;
 }