Add Log.h to replace all uses of iostream

On Android iostream doesn't appear in logcat, the system log that's
often used for printf debugging. Introduce Chromium/ANGLE like logging
that looks like the following:

  InfoLog() << stuff << stuff;

This makes sure the message is put in logcat on Android and removes
static initializers from <iostream>

BUG=dawn:286

Change-Id: Ie0d018f49bcac1a7b740739a6e59d45ae6728638
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/14102
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: David Turner <digit@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/common/Log.cpp

@@ -0,0 +1,112 @@
+// Copyright 2019 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "common/Log.h"
+
+#include "common/Assert.h"
+#include "common/Platform.h"
+
+#include <cstdio>
+
+#if defined(DAWN_PLATFORM_ANDROID)
+#    include <android/log.h>
+#endif
+
+namespace {
+
+    const char* SeverityName(LogSeverity severity) {
+        switch (severity) {
+            case LogSeverity::Debug:
+                return "Debug";
+            case LogSeverity::Info:
+                return "Info";
+            case LogSeverity::Warning:
+                return "Warning";
+            case LogSeverity::Error:
+                return "Error";
+            default:
+                UNREACHABLE();
+                return "";
+        }
+    }
+
+#if defined(DAWN_PLATFORM_ANDROID)
+    android_LogPriority AndroidLogPriority(LogSeverity severity) {
+        switch (severity) {
+            case LogSeverity::Debug:
+                return ANDROID_LOG_INFO;
+            case LogSeverity::Info:
+                return ANDROID_LOG_INFO;
+            case LogSeverity::Warning:
+                return ANDROID_LOG_WARN;
+            case LogSeverity::Error:
+                return ANDROID_LOG_ERROR;
+            default:
+                UNREACHABLE();
+                return ANDROID_LOG_ERROR;
+        }
+    }
+#endif  // defined(DAWN_PLATFORM_ANDROID)
+
+}  // anonymous namespace
+
+LogMessage::LogMessage(LogSeverity severity) : mSeverity(severity) {
+}
+
+LogMessage::~LogMessage() {
+    std::string fullMessage = mStream.str();
+
+    // If this message has been moved, its stream is empty.
+    if (fullMessage.empty()) {
+        return;
+    }
+
+    const char* severityName = SeverityName(mSeverity);
+
+    FILE* outputStream = stdout;
+    if (mSeverity == LogSeverity::Warning || mSeverity == LogSeverity::Error) {
+        outputStream = stderr;
+    }
+
+#if defined(DAWN_PLATFORM_ANDROID)
+    android_LogPriority androidPriority = AndroidLogPriority(mSeverity);
+    __android_log_print(androidPriority, "Dawn", "%s: %s\n", severityName, fullMessage.c_str());
+#else   // defined(DAWN_PLATFORM_ANDROID)
+    // Note: we use fprintf because <iostream> includes static initializers.
+    fprintf(outputStream, "%s: %s\n", severityName, fullMessage.c_str());
+    fflush(outputStream);
+#endif  // defined(DAWN_PLATFORM_ANDROID)
+}
+
+LogMessage DebugLog() {
+    return {LogSeverity::Debug};
+}
+
+LogMessage InfoLog() {
+    return {LogSeverity::Info};
+}
+
+LogMessage WarningLog() {
+    return {LogSeverity::Warning};
+}
+
+LogMessage ErrorLog() {
+    return {LogSeverity::Error};
+}
+
+LogMessage DebugLog(const char* file, const char* function, int line) {
+    LogMessage message = DebugLog();
+    message << file << ":" << line << "(" << function << ")";
+    return message;
+}